Boris Johnson pulls out of trip to Moscow

"United States intelligence indicates that Syrian military forces operating from this airfield were responsible for the chemical weapons attack on Syrian civilians in southern Idlib Province, Syria, that occurred on April 4", Trump wrote in the letter.

Russian Federation is the Syrian regime's main ally in the nation's six-year-long civil war.

It said the strike was believed to have been carried out by Russian planes, which operate in support of the Syrian government.

Prior to the attack, which killed almost 90 people, a senior State Department official said Tilllerson's meetings in Moscow on Wednesday would stress his core message that the USA is willing to work with Russian Federation in areas of practical co-operation that benefit Americans.

The Russia-Iran joint command said on Sunday that the U.S. military presence in northern Syria, where Washington is aiding its Kurdish and Arab allies against the Islamic State group, was an "illegal occupation".

He said that the Russian support for the Assad regime is deplorable, even after the suspected chemical attack.

Haley's remarks come just a day after she warned that the United States was prepared to take further actions in Syria during a special session at the UN following a USA military strike against a Syrian air base.

Sen. John McCain on Sunday lobbed part of the blame for Syria having used chemical weapons against its own citizens at President Trump and his administration.

Amid rising tensions between Moscow and Washington, Johnson said Saturday the situation in war-torn Syria had "fundamentally" changed following a chemical weapons attack on civilians and the USA airstrikes targeting a military airfield.

At the end of last month, Haley told reporters that the US priority in Syria "is no longer to sit there and focus on getting Assad out".

While, Washington stated it fired a barrage of 59 cruise missiles at the Shayrat base in response to what President Trump called a "barbaric" chemical attack on a rebel-held town on Tuesday that he blamed on the Damascus regime.

Mr Medvedev said the action taken by the Americans breached global law and their own internal procedures, and accused Washington of "barely avoiding combat clashes with Russia".

Many people welcomed the intervention from the United States, including Syrians, on social media, some of whom changed their profile pictures to an image of Mr Trump to show their support.

Cavusoglu, whose country is a strong backer of the Syrian opposition, said the most ideal process will be a political solution that leads to a transitional government accepted by all Syrians as soon as possible. Reports are that one woman was killed and several wounded in Saturday's attack. Shortly afterward, officials say the hospital was targeted.

"But where I differ from this administration, and I took the same position with respect to President Obama, we are a nation where you're not supposed to initiate military action, start war, without a plan that's presented to and approved by Congress", Kaine told Todd.