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As deadly airstrikes pounded Aleppo, Syria over the weekend, a major foreign ground force was also converging on the region. As many as 3,000 Iranian-backed fighters have arrived in Aleppo supporting the Syrian regime in its fight to crush the rebellion, two U.S. officials confirm to Fox News.

There are an estimated 250,000 Syrian civilians trapped in Aleppo facing an onslaught of Russian and Syrian bombs, according to reports. The Iranian-backed Shiite militias include fighters from neighboring Iraq as well as Afghanistan, officials say. Many of those fighters had already been in Syria but recently descended on Aleppo.

The Pentagon is not currently conducting any operations in Aleppo city, Capt. Jeff Davis toldreporters Monday. To date, U.S. policy has been to avoid getting entangled in Syria’s civil war, instead focusing on airstrikes against Islamic State targets largely in central and eastern Syria.

One year ago this week, Russia launched airstrikes in Syria in defense of President Bashar al-Assad. Russia took over a Syrian airport along the Mediterranean coast and deployed dozens of fighter jets and attack aircraft including helicopter gunships. President Obama said Russia and Iran's military actions in Syria in support of Assad would lead to a "quagmire."

Rescue workers said the weekend airstrikes were the worst Aleppo had seen in five years. More than 200 civilians have been killed in the past week, according to opposition activists.

Syrian Foreign Minister Walid al-Moallem said in a TV interview broadcast Monday that an internationally-brokered cease-fire was still viable. Al-Moallem, in the interview on Mayadeen TV from New York, also said Assad's administration was prepared to take part in a unity government, incorporating elements from the opposition, an offer that has been rejected in the past by his opponents.

The United Nations Security Council convened an emergency meeting Sunday but failed to take any action because of deep divisions between Russia and the Western powers. "What Russia is sponsoring and doing is not counter-terrorism, it's barbarism," said U.S. Ambassador Samantha Power. "It's apocalyptic what is being done in eastern Aleppo."

Britain's ambassador to the U.N., Matthew Rycroft, accused Russia of partnering with Syria to carry out war crimes, Sky News reported.

Al-Moallem accused the U.S., Britain, and France of convening the Security Council meeting in order to support "terrorists" inside Syria. But he said ongoing communications between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov meant a truce agreement brokered two weeks ago is "not dead."

Syria's military declared the cease-fire ended one week ago. The spokesman for Russian President Vladimir Putin said the cease-fire in Syria was ineffective, but that Moscow was not losing hope for a political solution to the country's crisis.

However, Dmitry Peskov told reporters Monday that the Kremlin is concerned that "terrorists are using the cease-fire regime to regroup, to replenish their arsenals and for obvious preparations to carry out attacks."

Peskov also took issue with harsh criticism by the United States and Great Britain over Russia's actions in Syria. He said Russia considers the tone of the criticism unacceptable and "such rhetoric is capable of causing serious harm to the resolution process" in Syria.

Al-Moallem's comments came as a second group of rebel gunmen and their families began evacuating from an opposition neighborhood in central Syria this month.

Some 120 gunmen and their families are expected to leave the al-Waer neighborhood in the central city of Homs as part of an agreement to restore the government's authority over the neighborhood, Homs Governor Talal Barazi said.

The developments further signal Assad's determination to settle the country's 5-1/2 year long war on his own terms, securing surrenders through sieges and staying in power at least through an interim period to steer the country out of crisis.

Pro-government forces have kept the al-Waer neighborhood under a steadily tightening siege since November 2013, prohibiting food and medical supplies from reaching the remaining 75,000 residents, down from 300,000 before the start of the war in 2011.

In exchange for the evacuations, the government is permitting aid convoys to supply the neighborhood with badly needed food and medical supplies. A Syrian Arab Red Crescent convoy of 36 trucks delivered assistance for 4,000 families in the district Saturday.

U.N. humanitarian officials have condemned the sieges against civilians as "medieval" and in contravention to international law.

In New York, al-Moallem reaffirmed his government's proposed roadmap to end Syria's war, saying Damascus would support a referendum on a new constitution followed by parliamentary elections and the formation of a unity government.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.