As Russia continues to bombard the northwestern Syrian province of Idlib from the skies, in support of the country’s ruling government’s campaign to retake territory, Washington is warning of retaliatory strikes.

Trump administration national security adviser John Bolton said this week that the US was in talks with France and the UK about possible air strikes targeting Syrian government assets.

“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 was quoted by The Wall Street Journal as saying.

The US has conducted two recent high-profile air strikes in Syria in response to alleged chemical-weapons attacks, once in April 2017 and again in April of this year.

The threat of force comes after Russia and Iran brushed off objections from the US and Turkey to back a Syrian operation to wrest Idlib from some 70,000 opposition militants.

One source close to the White House told Al-Monitor that the US administration was resigned to the Syrian offensive and acknowledged there were few options to stop it.

While officials in Washington, along with counterparts from European allies, are pre-emptively positioning to use chemical-weapons attacks as a pretense for possible air strikes, Russia has pointed the finger at the US for breaking international law with the use of white-phosphorus bombs.

Use of the incendiary white-phosphorus munitions in highly populated areas, such as Deir Ezzor where the purported strikes took place, is prohibited under international law.

The Pentagon denied Moscow’s accusations.

“None of the military units in the area are even equipped with white-phosphorus munitions of any kind,” Pentagon spokesman Commander Sean Robertson said.