U.S. Secretary of State Rex Tillerson issued a stern ultimatum to Russia Tuesday: side with America and its allies on Syria, or stand alongside Syrian President Bashar Assad, Iran and the militant group Hezbollah.

"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 following urgent meetings in Italy with top diplomats. "Or Russia can maintain its alliance with this group, which we believe is not going to serve Russia's interests longer term.

"We cannot let this happen again," he added.

The meeting of “likeminded” countries was arranged on the sidelines of the summit of the Group of 7 industrialized economies days after the U.S. launched airstrikes against Assad’s forces, and hours before Tillerson is scheduled to make a tense trip to Moscow to pressure Russia’s leaders to end their support for Assad.

Tillerson said it was unclear whether Russia had failed to take seriously its obligation to rid Syria of chemical weapons, or had merely been incompetent. But he said the distinction "doesn't much matter to the dead."

"It is clear to all of us that the reign of the Assad family is coming to an end," he said. "But the question of how that ends and the transition itself could be very important in our view to the durability, the stability inside of a unified Syria."

In addition to G-7 countries, diplomats at the summit are attending from Jordan, Qatar, Saudi Arabia, Turkey, the United Arab Emirates and others. The inclusion of the countries is important because the U.S. strategy for Syria involves enlisting help from Middle East nations to ensure security and stability in Syria after ISIS is defeated.

Diplomats made no remarks as photographers were allowed in briefly for the start of the meeting. The session lasted about an hour.

Tillerson, who has been largely out of the public eye, was visible during last week’s announcement of the response to the gruesome chemical attack, fielding questions from reporters on and off camera, and then captured in an official White House photo seated next to President Trump as they heard the result of the 59 cruise missiles that struck a Syrian military base.

Tillerson and U.S. officials have projected a sense of urgency about the Syria crisis, but have failed to set a strategy on how Assad must go, how to protect displaced Syrians and whether the U.S. should take further action. Successive attempts by top Trump administration officials to articulate a plan have only furthered the appearance of a policy still evolving.

"We rededicate ourselves to holding to account any and all who commit crimes against the innocents anywhere in the world," Tillerson said Monday while visiting Sant'Anna di Stazzema, a Tuscan village where the Nazis massacred more than 500 civilians during World War II.

Leading up to the U.S. missile attack, Trump's administration had said that Assad's future was up to the Syrian people. Then Trump, the day after the assault, said his thinking about Assad had changed. Tillerson answered a question about effecting regime change by saying the U.S. was organizing a coalition to do just that.

The Associated Press contributed to this report.

