U.S. Ambassador to the United Nations Nikki Haley Nimrata (Nikki) Haley'The soul' versus 'law and order' Author Ryan Girdusky: RNC worked best when highlighting 'regular people' as opposed to 'standard Republicans' GOP lobbyists pleasantly surprised by Republican convention MORE slammed Russia over a deadly chemical attack on Syrian civilians, saying the country's hands are "covered in blood."

"The Russian regime, whose hands are all covered in the blood of Syrian children, cannot be ashamed by pictures of its victims," Haley said during a U.N. Security Council meeting on Monday.

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"We must not overlook Russia and Iran's roles in enabling the Assad regime's murderous destruction," she continued.

Russia and Iran have been strong supporters of Syrian President Bashar Assad's government.

Haley also took aim at Assad.

"Only a monster does this. Only a monster targets civilians and ensures there are no ambulances to transfer the wounded. No hospitals or medicine to ease their pain," she said.

“The monster who was responsible for these attacks has no conscious," she added.

Dozens of Syrian civilians were killed on Saturday during a reported chemical attack on the rebel-held Syrian city of Douma, which is about 10 kilometers northeast of Damascus.

The Syrian government and the Kremlin have denied involvement in the attack.

Russian envoy to the U.N. Vassily Nebenzia said on Monday the attack was staged, and that any U.S. military response could have "grave repercussions."

"There was no chemical weapons attack," Nebenzia told the Security Council.

“Russia is being unpardonably threatened," he said. “The boorishness against my country is unacceptable and exceeds Cold War standards."

Tensions between the U.S. and Russia have intensified following the attack.

President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE condemned the attack in a tweet on Sunday, even calling out Russian President Vladimir Putin by name.

Trump on Monday said that he would make his decision on how to respond to Syria in the next "24 to 48 hours," calling the chemical attack "heinous."

Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price... — Donald J. Trump (@realDonaldTrump) April 8, 2018

....to pay. Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK! — Donald J. Trump (@realDonaldTrump) April 8, 2018

Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE on Monday did not rule out military action against Syria.

“The first thing we have to look at is why are chemical weapons still being used at all when Russia was the framework guarantor of removing all the chemical weapons,” Mattis said.