The United States says it has identified "potential preparations" for a chemical attack by Syrian government forces similar to an April attack in northern Syria that prompted U.S. airstrikes in response.
A statement late Monday from White House press secretary Sean Spicer warned Syrian President Bashar al-Assad that if government forces do carry out another chemical attack, then "he and his military will pay a heavy price."
There was no specific information or evidence presented about the alleged preparations.
Syrian officials denied the allegations.
U.S. Ambassador to the U.N. Nikki Haley wrote on Twitter that any further attacks against Syrian civilians "will be blamed on Assad, but also on Russia and Iran who support him killing his own people."
Russia and Iran are Assad's main backers, and have provided military support in the complex fight against both rebels and Islamic State militants.
Russian presidential spokesman Dmitry Peskov told reporters Tuesday threats against the Syrian leadership are "unacceptable," and that he did not know of any information about a threat for a chemical attack.
The April 4 attack on the opposition-held town of Khan Sheikhoun killed more than 80 people. Analysis by the French government found that sarin gas was used along with a stabilizer known as hexamine, and that the same manufacturing process was used for a 2013 chemical attack attributed to the Syrian government.
Assad has rejected that his forces were responsible for what happened in Khan Sheikhoun, saying the incident was a "fabrication" the United States used to justify a military strike against Syrian forces.
The U.S. strikes hit a Syrian airbase believed to be the source of the chemical weapons.
British Defense Secretary Michael Fallon said in an interview Tuesday with Sky News that his government would back another similar strike, and that he plans to discuss the situation with U.S. Defense Secretary Jim Mattis during a meeting Thursday in Brussels.
"We fully supported the last strike that took out the airplanes and the support that they required to drop chemical weapons, and if the United States is considering a similar strike, then we will support that, too," Fallon said.
Regional analyst Anthony Billingsley of the University of New South Wales told VOA he fears that with the recent shooting down of a Syrian jet and a Russian threat to treat planes from a U.S.-led coalition as hostile, another retaliatory strike could be "a much more serious danger."
"We’re now starting to add to the sort of militarization of this particular tension between governments, and that’s very worrying because these things can suddenly lose control and get out of hand," Billingsley said.