WASHINGTON -- The U.S. has no evidence that Russia was involved in last week’s fatal sarin gas attack in Syria, but Russia’s “failure” allowed the deaths of innocent people, Secretary of State Rex Tillerson said, ahead of his visit to Moscow.

“Well, to our knowledge, we do not—we do not have any information that suggests that Russia was part of the military attack undertaken using the chemical weapons,” Tillerson said Sunday on CBS News’ “Face the Nation,” amid reports that the U.S. is investigating possible Russian connection to the deadly sarin gas attack.

That doesn’t mean Russia is without fault, Tillerson said. He said Russia in 2013 gave “certain assurances” under an agreement with the U.S. and in accordance with U.N. Security Council resolutions that it would be “the guarantor of the destruction of Syria’s chemical weapons, stockpiles.”

“Russia has failed in that commitment,” he said. “And the result of their failure has led to the killing of more children and innocents.”

Tillerson offered more criticism, saying the Russians, “have played now for some time the role of providing cover for Bashar al-Assad’s behavior.”

U.S. Ambassador to the U.N. Nikki Haley had a stronger message for Russia last week, saying, “How many children have to die before Russia cares?”

Tillerson said he isn’t afraid of Russian retaliation after the U.S. strike last week on a Syrian airfield.

“I see no reason that there would be retaliation since the Russians were never targeted in this particular strike,” Tillerson said. “It was a very deliberate, very proportional, and — and very targeted strike undertaken in response to the chemical weapons attack. And Russia was never part of the targeting.”

Tillerson also responded to Sen. Marco Rubio, R-Florida, who said last week that Tillerson is “nodding to the idea that Assad was going to get to stay in some capacity” by saying the Syrian people, not the U.S., will decide their own fate.

“I think that’s a regrettable comment on the part of Senator Rubio,” Tillerson said.

Tillerson’s comments come days before he is set to meet with Russian Foreign Minister Sergei Lavrov about a range of international security issues, including the situations in Syria, North Korea and Ukraine.

Tillerson also shed light on President Donald Trump’s meeting with Chinese President Xi Jinping last week at Mr. Trump’s Mar-a-Lago resort in Florida, where both presidents had “extensive discussions around the dangerous situation in North Korea,” Tillerson said. North Korea continues to ignore warnings not to develop or test nuclear weapons.

“I think it was a very useful and productive exchange,” Tillerson said. “President Xi clearly understands, and — and I think agrees, that the situation has intensified and has reached a certain level of threat that action has to be taken.”

“And, indeed, the Chinese, even themselves, have said that they do not believe the conditions are right today to engage in discussions with the government in Pyongyang,” Tillerson continued. “And so what I think we’re hopeful is that we can work together with the Chinese to change the conditions in the minds of—of the DPRK leadership. And then, at that point, perhaps discussions may be useful. But I think there’s a shared view and no disagreement as to how dangerous the situation has become. And I think even China is beginning to recognize that this presents a threat to even — to— to China’s interests as well.”