FILE PHOTO: U.S. President Donald Trump's national security adviser John Bolton speaks at a news conference in Kiev, Ukraine August 24, 2018. REUTERS/Valentyn Ogirenko

WASHINGTON (Reuters) - President Donald Trump’s national security adviser said on Monday the United States, Britain and France had agreed that another use of chemical weapons by the Syrian government would result in a “much stronger response” compared to previous air strikes.

“We’ve tried to convey the message in recent days that if there’s a third use of chemical weapons, the response will be much stronger,” national security adviser John Bolton said while fielding questions after a policy speech.

“I can say we’ve been in consultation with the British and the French, who joined us in the second strike, and they also agree that another use of chemical weapons will result in a much stronger response,” Bolton said.

U.S. officials have said in recent days they have evidence that Syrian government forces are preparing chemical weapons ahead of a planned assault on a rebel-held enclave in Idlib in the northwestern part of the country.

Marine General Joseph Dunford, the chairman of the Joint Chiefs of Staff, told reporters late last week he was involved in a routine dialogue with the White House about military options should Syria ignore U.S. warnings against using chemical arms.

Syrian President Bashar al-Assad has massed his army and allied forces on the front lines in the northwest, and Russian planes have joined his bombardment of rebels there, in a prelude to a widely expected assault despite objections from Turkey.

Bolton, after a speech condemning the International Criminal Court, said the judicial body’s failure to act in response to earlier chemical weapons attacks was evidence that it was ineffectual in deterring war crimes.

He also dismissed claims that U.S. actions against Syria encouraged al Qaeda rebels to use chemical weapons and blame the attacks on the Damascus government.

“The government of Russia and others have said that we are giving the authorization for al Qaeda to use chemical weapons and try and pin it on the government of Syria,” Bolton said on the eve of the Sept. 11, 2001 attacks on the United States. “That has to be, in the history of propaganda in the 20th and 21st centuries, one of the most outrageous claims that I can think of.”