The Pentagon reportedly said on Tuesday that the U.S. has observed chemical weapons activity at a Syrian air base used to launch the April chemical attack that left dozens of civilians dead.

Pentagon spokesman Capt. Jeff Davis said that the U.S. has seen “active preparations for chemical weapons use,” according to the Associated Press.

It was not immediately clear if another chemical strike by the Syrian government is imminent, but the last prompted President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE to launch a missile strike.

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The White House said in a statement Monday night that the U.S. had identified potential preparations for a chemical strike by the regime of Syrian President Bashar Assad, and warned the Syrian government against conducting another attack.

"As we have previously stated, the United States is in Syria to eliminate the Islamic State of Iraq and Syria," press secretary Sean Spicer Sean Michael SpicerKellyanne Conway to leave White House at end of month Pro-Trump duo Diamond and Silk launch new program on Newsmax TV The Hill's 12:30 Report - Presented by Facebook - Supreme Court's unanimous decision on the Electoral College MORE said. "If, however, Mr. Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price."

Syria's government as well as Russia, which backs Assad, rejected the White House's allegations on Tuesday.

A chemical strike allegedly carried out by the Assad regime in April left dozens of civilians dead, many of them children.

That attack prompted President Trump to launch a strike on the Syrian government's Shayrat airfield, from which the chemical attack was believed to originate.