“I think the real failure here has been Russia’s failure to live up to its commitments under the chemical weapons agreements that were entered into in 2013,” Tillerson said on ABC’s This Week.

“The failure related to the recent strike and the recent terrible chemical weapons attack in large measure is a failure on Russia’s part to achieve its commitment to the international community,” he added.

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

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He stopped short of accusing Russia of being directly involved in the planning or execution of the attack, saying he had not seen “any hard evidence” 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 because “every time one of these horrific attacks occurs, it draws Russia closer into some level of responsibility.”

Other than that, he added, “there is no change to our military posture” towards Syria.

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Tillerson’s comments came just a few days after the United States fired dozens of cruise missiles at the Syrian airbase that was allegedly used in the chemical attack.

U.S. President Donald Trump ordered the strikes after he blamed Assad for this 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 U.S.-Russian relations.