WASHINGTON, April 9 (Xinhua) -- U.S. President Donald Trump on Monday said the United State will make "major decisions" over the reported chemical weapon attack in Syria soon, and warns "tough" consequence for Russian President Vladimir for the incident.

Trump said in a cabinet meeting that the attack was "heinous", "atrocious", "barbaric" and "horrible," noting "we'll be making some major decisions over the next 24 to 48 hours."

"As bad as the news is around the world, you just don't see those images," he said. "We are studying that situation extremely closely ...we're looking at that very, very strongly and very seriously."

Speaking of his earlier claim to get the U.S. troops out of Syria soon, Trump said "we'll be making that decision very quickly, probably by the end of today."

He said that "nothing's off the table," referring to the possible U.S. military action against Syria.

In the unusual rhetoric against Russia, Trump added that Putin "may" bear responsibility for the Syrian incident.

"If he does, it's going to be very tough. Very tough," he said. "Everybody's going to pay a price. He will, everybody will."

He also hinted that Syria, Iran and Russia are behind the attack.

"They're saying they're not. But, to me, there's not much of a doubt. But the generals will figure it out, probably over the next 24 hours," said Trump.

Earlier on Monday, U.S. defense chief James Mattis said Washington has not ruled out launching airstrikes against Damascus.

"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 chemical weapons, and so working with our allies and partners from NATO to Qatar and elsewhere we are going to address this issue," Mattis said.

U.S. media reported that National Security Council principals are holding a "small group" meeting to discuss Syria on Monday, led by John Bolton on his first official day as White House national security adviser.

U.S. bilateral relations with Russia have deteriorated recently due to the U.S. expulsion of Russian diplomats and sanctions of Russian business leaders and high-ranking officials. The incident in Syria was expected to be a new flashpoint between the two nations.

Trump on Sunday condemned Syria, Russia and Iran for what he called the "SICK" attack, threatening "big price to pay." The unexpected rhetoric has sparked concerns over the prospect of the U.S. withdrawal of troops from Syria that Trump has reiterated recently.

Also on Sunday, Trump spoke over phone with his French counterpart Emmanuel Macron, agreeing on a "strong, joint response" to the alleged chemical weapons attack in Syria.

The two leaders also "agreed to exchange information on the nature of the attacks and coordinate a strong, joint response," according to the statement released by the White House.

Activists, local rescuers and rebels in Syria have claimed that Syrian forces used chlorine gas in the attack on Saturday against Douma, in the rebel-held area near Damascus.

The Syrian Foreign Ministry responded to the rebels' claims of chemical weapons use by the Syrian army in Douma district near Damascus as "premeditated pretexts," according to state news agency SANA.

The ministry said the allegations have been planned beforehand to prolong the lives of the "terrorists" in Douma. The Syrian government has denied the allegations and called it fake news.

Earlier on Monday, the Organization for the Prohibition of Chemical Weapons (OPCW) said it was investigating the incident and has made a preliminary analysis of the reports of the alleged use of chemical weapons.

The Russian Foreign Ministry on Sunday refuted reports purporting that Syrian government forces used chemical weapons in Douma district, a besieged enclave near capital Damascus, calling the allegation "fabrication" and "provocation."

Speaking at the UN Security Council briefing on the situation in the Middle East, Wu Haitao, China's deputy permanent representative to the UN, said that China firmly opposes the use of chemical weapons under any circumstances, adding that his country is "greatly concerned by the use of chemical weapons against civilians in Syria."

All parties should continue to insist that the Security Council and the Organization for the Prohibition of Chemical Weapons (OPCW) should be the main channels for addressing the use of chemical weapons, said the Chinese envoy.

Wu expressed the hope that the Syrian government would continue to cooperate with OPCW on the resolution of the initial declaration and properly resolve the outstanding issues.