Former U.S. Ambassador to the United Nations Nikki Haley said Monday that Russian President Vladimir Putin and other autocrats know Joe Biden is "the weakest president in history" and therefore understand that if they want to take drastic actions like invading Ukraine, "this is the time to do it."

Haley, a former South Carolina governor, told "Special Report" it was important for Biden to meet with Germany's new left-leaning chancellor, Olaf Scholz – as Berlin is in a sensitive diplomatic position given its place in NATO and Western democracy while also being reliant on Russian energy.

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The United States and Germany announced their "united approach" to deterring further Russian aggression against Ukraine, with President Biden warning that the Nord Stream 2 pipeline will not be operational if Russia follows through with an invasion of Ukraine.

Biden welcomed German Chancellor Olaf Sholz to the White House for his first official visit to Washington on Monday for what he described as a "very productive meeting" in which the two discussed their countries' "shared values that shape how each of us approaches leadership."

Both Biden and Scholz, during a joint press conference Monday, said they spent a significant amount of time discussing the situation between Russia and Ukraine, maintaining their preference to pursue a diplomatic approach to prevent an incursion.

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President Biden made clear that the Nord Stream 2 pipeline will not go online if Russia follows through with an invasion of Ukraine.

"If Russia invades, that means tanks with troops crossing the border of Ukraine... there will be no longer a Nord Stream 2," Biden said during a joint press conference with Chancellor of Germany Olaf Scholz.

Scholz said that his country was committed to working in lockstep with the U.S. on the issue of Russia, though he did not specifically point to a shutdown of the controversial pipeline.

Denis Pushilin, the leader of the Donetsk People's Republic in eastern Ukraine, said during an interview Monday that a full-scale war could erupt at any moment, according to Reuters.

"First of all we rely on ourselves, but we do not rule out that we will be forced to turn to Russia if Ukraine, with the support of Western countries, passes a certain line," he reportedly said.

"It could all start at any moment, regardless of weather conditions," Pushilin added. "Sometimes unfavourable weather conditions are good cover for launching an attack."

A Ukrainian serviceman holds a heavy machine gun at a frontline position in the Luhansk region, eastern Ukraine, on Monday. (AP/Vadim Ghirda)

Alexander Khara, a former Ukrainian defense official, told Al Jazeera in an interview Monday that "it’s going to be a bloody hell for the Russians" if Moscow decides to launch an invasion of Ukraine.

"See, if they decide to cross [the border] and especially if they then decide to enter our cities… Thanks to the British, we have pretty powerful anti-tank missiles that can be used in urban warfare, and certainly, we have enough of our own to deploy," Khara said.

"War was imposed on us, we are going to fight back, and I haven’t seen any sign of Ukrainian society being tired of war or [preparing to] capitulate to Russian demands," he added.

Khara also told the news outlet that he sees "no room for diplomacy" with the current standoff between the two sides, as "[Russia wants us to be] a sort of pro-Russian buffer zone, and that’s not going to happen."

"Secondly, they’re trying to use Ukraine as a leverage against the European Union and NATO, to divide the Europeans between themselves and Europeans from the Americans," he said.

Former assistant secretary of state Robert Charles discusses the U.S. response to growing tensions between Russia and Ukraine and what is expected next.

KYIV, Ukraine – Despite the dire warnings from the White House and Pentagon over the growing number of Russian forces on Ukraine’s border and what is being billed as a pending invasion "any day," Ukraine’s leaders are telling their people to "keep calm." 

Two hours north of Ukraine’s capital in an abandoned city outside Chernobyl decades after one of the world’s worst nuclear disasters, Ukrainian forces trained for urban combat in freezing temperatures inside deserted buildings. Fox News attended the live-fire training, which included ambush, sniper, mortar, evacuation and advanced firefighting scenarios. 

Some 30,000 Russian troops, dozens of attack jets and fourth-generation air defense systems have now massed on Ukraine’s border not far from Chernobyl in neighboring Belarus to the north, according to U.S. officials. Asked by a Fox News reporter if he was concerned Russian forces would be invading from Belarus, less than 100 miles from Kyiv, Ukraine’s capital city, the country’s defense chief did not appear worried.

"I am not concerned," said Oleksii Reznikov, Ukraine’s defense minister.  "I am very, very sure that the Ukrainian Armed Forces are ready for deterrence, for resilience. The Ukrainian people are also ready for deterrence."  

"The word ‘imminent’ doesn’t work," he added. "Keep calm." 

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German Chancellor Olaf Scholz smiles at journalists traveling with him in the Air Force Airbus A340 on the way to Washington where he will meet President Biden at the White House. (Photo by Kay Nietfeld/picture alliance via Getty Images)

President Biden is set to meet with German Chancellor Olaf Scholz on Monday and one of the key topics will be Russia and what a united front would look like with Berlin, which critics have accused of not taking a firm position on the matter.

Scholz told the Washington Post in an interview on Friday that Russia will face “high prices” if it decides to invade.

The Biden administration said that the controversial Nord Stream 2 pipeline will not move forward if Russia invades. 

Scholz said Berlin is willing to take “all necessary steps” to prevent a conflict. 

“And we have a very clear agreement with the United States government on gas transit and energy sovereignty in Europe,” he told the paper. “We already also agreed that we will support Ukraine, that we will fight for the gas transit via Ukraine intensely and that we will be very strong if this gas transit would be endangered. Also, it is absolutely clear that in a situation like this all options are on the table. Please understand that I will not get into any specifics, but our answer will be united and decisive.” -Edmund DeMarche

French President Emmanuel Macron during a joint press conference with German Chancellor Olaf Scholz ahead of talks at the Chancellery on January 25, 2022 in Berlin. (Photo by Kay Nietfeld - Pool/Getty Images)

Emmanuel Macron, the French president, is en route to Moscow on Monday to meet with Russian President Vladimir Putin as tension on Ukraine’s eastern border approaches its highest levels. 

Reuters reported that Macron’s decision to meet with Putin is a “risky diplomatic move” and can “prove embarrassing if he returns empty-handed.” 

Turkish President Recep Tayyip Erdogan tried his hand last week at being a mediator between the two countries but came up empty. Erdogan said the U.S. and other Western countries have done nothing to bring down the temperature in the region. 

“When we look at…the United States, Biden has not yet shown a positive approach to the matter,” he said, according to Reuters. 

Macron has been interacting with other Western leaders—including President Biden during calls last weekend and said he believes he can score an “historic solution.”

Macron told a French paper that Moscow wants a clarification of the rules when it comes to NATO. 

“The intensity of the dialogue we have had with Russia and this visit to Moscow are designed to stop that happening,” Macron said, according to the Guardian. “Then we will discuss the terms of de-escalation. We have to be very realistic. We will not obtain unilateral gestures, but it’s essential to stop the situation deteriorating.” -Edmund DeMarche

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National security adviser Jake Sullivan said that while the U.S. is prepared for multiple scenarios involving Russia and Ukraine, there are a number of subjects they are willing to discuss when it comes to a possible deal with the Kremlin.

As Russia continues to amass troops near the border with its neighbor, the Biden administration continues to hold out hope that a diplomatic solution can be reached. In an appearance on "Fox News Sunday," Sullivan hinted at what that could look like. - Ronn Blitzer