WASHINGTON (REUTERS) - US Secretary of State Rex Tillerson on Sunday (April 8) blamed Russia's inaction for helping fuel a deadly poison gas attack against Syrian civilians last week, saying Moscow failed to carry out a 2013 agreement to secure and destroy chemical weapons in Syria.

Appearing on CBS' Face the Nation, Mr Tillerson said, "The Russians have played now for some time the role of playing cover for Bashar al-Assad's behaviour."

Mr Tillerson is expected in Moscow this week for talks with Russian officials.

He stopped short of accusing Russia of being directly involved in the planning or execution of the attack, saying he had not seen any information to suggest the nation was an accomplice to Syrian President Bashar al-Assad.

But he said the United States expected Russia to take a tougher stance against Syria by rethinking its alliance with al-Assad.

Mr Tillerson's comments came just a few days after the US fired dozens of cruise missiles at the Syrian airbase that was allegedly used in the chemical attack. US President Donald Trump ordered the strikes after he blamed Assad for last week's chemical attack, which killed at least 70 people, many of them children, in the Syrian town of Khan Sheikhoun.

The Syrian government has denied it was behind the attack.

Video depicted limp bodies and children choking while rescuers tried to wash off the poison gas.

Russian state television blamed rebels and did not show footage of victims.

The move immediately prompted a backlash from Russian President Vladimir Putin, who said it would damage US-Russian relations.