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One of the top Republican lawmakers in the House joined on Sunday a growing list of legislators calling on the Trump administration to explain what it knew about the reports that Russian intelligence agents offered to pay bounties to Afghan militants who killed U.S. troops in the country.

House Republican Conference Chairwoman Liz Cheney of Wyoming tweeted Sunday morning that if the reports in the New York Times about the bounties were true, then the White House needed to explain what it knew about the intelligence and how it responded.

A senior official told CBS News the bounty allegations did not appear in the President's Daily Brief, a regular summary of national-security issues delivered to the president and some Cabinet secretaries. The National Security Council has been performing "due diligence" but has not found the intel assessment as described in the existing reporting, the official said.

Cheney, the third-ranking Republican in the House, specifically focused on the denials by both Trump and White House staff that neither the president nor Vice President Pence were briefed on the matter, and asked for more information on why this is the case.

"If reporting about Russian bounties on US forces is true, the White House must explain: 1. Why weren’t the president or vice president briefed?" Cheney tweeted. "Was the info in the PDB? 2. Who did know and when? 3. What has been done in response to protect our forces & hold Putin accountable?"

The New York Times first reported over the weekend that American intelligence officials have determined a Russian military unit secretly offered bounties to Taliban-linked militants for killing coalition forces, including targeting American troops. The Wall Street Journal and Washington Post also reported on the Kremlin's effort to orchestrate attacks on Western troops.

The Times reported that President Trump and the White House's National Security Council were briefed on Russia's bounty rewards in late March. They discussed an appropriate response, ranging from making a diplomatic complaint to Moscow and economic sanctions, but the White House had not yet authorized a response.

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Lawmakers on both sides of the political divide have called on the Trump administration to explain what it knew about the bounties.

Sen. Lindsey Graham, R-S.C., said it's "imperative" to get answers and urged the Trump administration to tell Congress what it knows about Russia's efforts to pay bounties to kill American soldiers.

"I expect the Trump Administration to take such allegations seriously and inform Congress immediately as to the reliability of these news reports," Graham, the chairman of the House Judiciary Committee and member of the Senate Foreign Relations Committee, tweeted.

Sen. Tim Kaine, D-Va., questioned how Trump could hold an amicable relationship with Russian President Vladimir Putin -- even welcoming him to a G-7 Summit in America -- while his regime was reportedly trying to kill Americans.

"President Trump was cozying up to Putin and inviting him to the G7 all while his Administration reportedly knew Russia was trying to kill U.S troops in Afghanistan and derail peace talks with the Taliban," Kaine, the 2016 Democratic vice presidential nominee, tweeted.

The White House, however, said Saturday that Trump was not briefed on the alleged Russian bounty intelligence, but didn't confirm or deny the underlying reporting that Russia was giving out rewards to attack U.S. soldiers.

Trump on Sunday added his own denial of being briefed, saying in a tweet that neither he nor Pence or White House Chief of Staff Mark Meadows had been notified of the bounties, and questioned the veracity and sourcing of the New York Times’ article.

"Nobody briefed or told me, @VP Pence, or Chief of Staff @MarkMeadows about the so-called attacks on our troops in Afghanistan by Russians, as reported through an "anonymous source" by the Fake News @nytimes," Trump tweeted.

He added: "Probably just another phony Times hit job, just like their failed Russia Hoax. Who is their ‘source’?"

The reporting quickly became fodder for the 2020 presidential campaign.

During a town hall Saturday, former Vice President Joe Biden brought up the "shocking revelation" that Trump reportedly knew of the bounties for months and slammed the president for doing "worse than nothing."

"Not only has he failed to sanction or impose any kind of consequences on Russia for this egregious violation of international law, Donald Trump has continued his embarrassing campaign of deference and debasing himself before Vladimir Putin," Biden, the presumptive Democratic presidential nominee, said. "He has had this information according to the Times, and yet he offered to host Putin in the United States and sought to invite Russia to rejoin the G7.  His entire presidency has been a gift to Putin."

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Sunday morning, Trump fired back at Biden, reiterating his position that Russia took advantage of him and Obama during the previous administration.

"Funny to see Corrupt Joe Biden reading a statement on Russia, which was obviously written by his handlers," Trump tweeted. "Russia ate his and Obama’s lunch during their time in office, so badly that Obama wanted them out of the then G-8. U.S. was weak on everything, but especially Russia!"

The Lincoln Project, a Republican super-PAC that is highly critical of Trump, also took aim at the president’s denial.

"This heinous failure by the commander-in-chief to protect American soldiers in the field is unthinkable," Reed Galen, co-founder of the anti-Trump group, said in a statement. "There aren’t words to describe Donald Trump’s dereliction of duty as Commander in Chief."

"Congress should charge him for this crime," co-founder Mike Madrid added. "Unfortunately, his enablers in the U.S. Senate, starting with Majority Leader Mitch McConnell, will shrug off this war crime like he has everything else."

Fox News’ Marisa Schultz contributed to this report.