A White House official said on Tuesday that relevant agencies, including the Pentagon, the State Department, the C.I.A. and the Office of the Director of National Intelligence, had been involved in issuing the statement.
A defense official said that Defense Secretary Jim Mattis was aware of the movements at Al Shayrat and that the White House statement was coming. The situation âwas very fast-moving,â the official said on Tuesday.
It remained unclear whether the statement was based on raw intelligence that President Trump had chosen to declassify. Neither White House nor Pentagon officials said an attack, or retaliation, was imminent in Syria, where the United States is backing Syrian fighters battling the Islamic State militants amid the countryâs six-year civil war.
âThe Department of Defense remains focused on operations to defeat ISIS,â Maj. Adrian Rankine-Galloway, a Defense Department spokesman, said in a statement, using an acronym for the Islamic State. âNevertheless, the continued brutality of the Assad regime and his use of chemical weapons presents a clear threat to regional stability and security, as well as the national security interests of the United States and our allies.â
In Damascus, Ali Haidar, the Syrian minister for national reconciliation, was quoted by The Associated Press as saying on Tuesday that the government did not have chemical weapons and that it would not use any. He accused the White House of releasing the statement to pave the way for a âdiplomatic battleâ against Syria at the United Nations.
Officials in Russia, which has provided military and political support to Mr. Assad during the Syrian conflict, also rejected the accusations.
âI am not aware of any information about a threat that chemical weapons could be used,â Dmitri S. Peskov, the Kremlin spokesman, said on Tuesday. âCertainly, we consider such threats to the legitimate leadership of the Syrian Arab Republic unacceptable.â
A senior Russian lawmaker accused the United States of using the declaration about chemical weapons to plan an attack on Syria.
âPreparations for a new cynical and unprecedented provocation are underway,â Frants Klintsevich, first deputy chairman of the defense and security committee in the upper chamber of the Russian Parliament, told the state-owned news agency RIA Novosti.
As if to punctuate his contempt for the Trump administrationâs warning, President Bashar al-Assad visited a Russian air base near Latakia in the western part of the country on Tuesday, accompanied by Gen. Valery V. Gerasimov, the Russian militaryâs chief of staff. Syrian news media, which reported the visit, also distributed a video clip of Mr. Assad climbing into the cockpit of a Russian Sukhoi Su-35 parked at the base, where Russia has conducted many of its bombing operations to support the governmentâs side in the war.
The United States and other world powers have accused Mr. Assadâs forces of repeatedly using chemical weapons to subdue rebels seeking to topple his government. Chemical attacks killed more than 1,000 people near Damascus in 2013 and dozens more in northern Syria in April of this year.
Mr. Trump has taken a different approach to the use of chemical weapons in Syria than his predecessor, President Barack Obama, did. After the 2013 attack, Mr. Obama declined to strike the Syrian government, despite having declared the use of chemical weapons a âred line.â Instead, he agreed to a deal, proposed by Russia, for the Syrian government to dispose of its chemical weapons stockpiles and manufacturing capabilities.
But American officials suspect that Syria kept some of its chemical weapons capabilities.
At the United Nations on Tuesday, the ambassadors of France and Britain, which supported the Tomahawk strike two months ago, declined to comment on the White Houseâs latest warning. But FranÃ§ois Delattre, the French ambassador, told reporters that another chemical weapons assault in Syria would cross âa very clear red line on our side.â
âWhat is at stake is the future of the nonproliferation regime,â he said. âSo any weakness on this would open the Pandoraâs box and leave the nonproliferation architecture as a whole weakened and threatened. This is something we canât afford.â