"We want to relieve suffering of Syrian people," - Tillerson to propose Russia siding with US allies or maintain alliance with Syria, Iran

U.S. Secretary of State Rex Tillerson arrived in Moscow Tuesday following his Monday's claim that Washington has concluded Russia knew in advance of Syria's chemical weapons attack.

As reported by Censor.NET citing Assosiated Press, Tillerson is set to deliver Russia an ultimatum: Side with the U.S. and likeminded countries on Syria, or embrace Iran, militant group Hezbollah and embattled Syrian leader Bashar Assad.

"We cannot let this happen again," Tillerson said of the chemical attack.

"We want to relieve the suffering of the Syrian people. Russia can be a part of that future and play an important role," Tillerson added in remarks to reporters. "Or Russia can maintain its alliance" with Syria and Iran.

Russian President Vladimir Putin immediately showed that he wouldn't back down, saying Russia knew about planned "provocations" to blame Syria's government for using chemical weapons. He said the U.N. should first investigate the attack.

"It reminds me of the events in 2003 when U.S. envoys to the Security Council were demonstrating what they said were chemical weapons found in Iraq," Putin told reporters on Tuesday. "We have seen it all already."

Tillerson is in Moscow to meet with Russian officials about the Syria civil war. It is the first official trip to Russia by a member of President Donald Trump's Cabinet. It's unclear if Putin and Tillerson will meet.

Before heading to Russia, Tillerson told reporters that Moscow had either failed to take seriously its obligation to rid Syria of chemical weapons, or had been incompetent. But, he said, the distinction "doesn't much matter to the dead."

It wasn't clear what the punishment would be for a Russian government that has used its military might to help Assad and his array of allies score a series of battlefield successes in their six-year war with Syrian opposition groups.

Russia's foreign ministry said in a statement that it hoped for "productive talks." It said the outcome of the discussions is important not only for the U.S.-Russian relationship, but "for the overall atmosphere on the world stage."