U.S. intelligence intercepted communications between Syrian military, chemical experts

The U.S. military and intelligence community intercepted communications featuring Syrian military and chemical experts talking about preparations for the sarin attack in Idlib last week, a senior US official tells CNN.

The intercepts were part of an immediate review of all intelligence in the hours after the attack to confirm responsibility for the use of chemical weapons in an attack in northwestern Syria, which killed at least 70 people.

U.S. officials have said that there is "no doubt" that Syrian President Bashar al-Assad is responsible for the attack.

The U.S. did not know prior to the attack it was going to happen, the official emphasised.

So far, there are no intelligence intercepts that have been found directly confirming that Russian military or intelligence officials communicated about the attack.

President Donald Trump told a White House news conference on Wednesday that the Pentagon is looking into the question of Russian complicity in the chemical attack.

"I would like to think that they didn't know, but certainly they could have," Trump said. "Defence Secretary Gen. James Mattis is looking into it with the entire Pentagon group that does that kind of work.