The United States will stand up against anyone who commits crimes against humanity, U.S. Secretary of State Rex Tillerson said on Monday, less than a week after Washington launched missile strikes in response to a reported Syrian chemical attack.

"We rededicate ourselves to holding to account any and all who commit crimes against the innocents anywhere in the world," Tillerson told reporters while commemorating a German Nazi massacre committed in Italy in 1944.

The U.S. attacked the Syrian air base last Friday in retaliation for what it said was a chemical weapons assault on April 4 by Syrian President Bashar al-Assad that killed dozens of civilians, including many children.

Tillerson is in Italy for an annual meeting for the Group of Seven major industrialized nations. Foreign ministers were expected to to seek clarity from the United States on an array of issues, especially Syria.

The two-day meeting in the Tuscan walled city of Lucca is the first for the G7 since Donald Trump became U.S. president and comes at a moment when the United States is sending a Navy carrier strike group toward the Korean Peninsula to provide a physical presence following North Korea's persistent ballistic missile tests.

But the civil war in Syria is likely to dominate talks, with Italy hoping for a final communiqué that will reinforce United Nations' efforts to end six years of conflict.

Freeland told CBC's Power and Politics on April 7, "now it's time to push even harder for a diplomatic solution and time to apply real pressure on the Syrian regime and on its patrons, Russia and Iran, to recognize a war crime was committed this week. It's time for them to get to the table, it's time for this war to end."

"Now it's time for the international community, in particular Canada with the United States and with our G7 allies, with our NATO allies, to talk about next steps," she said.

Canadian Foreign Minister Chrystia Freeland, who is attending the G7 meeting in Italy, is shown speaking to reporters on March 31 at a meeting of NATO foreign ministers in Brussels on March 31. (Virginia Mayo/AFP/Getty Images)

The meeting will give Italy, Germany, France, Britain, Canada and Japan their first chance to grill Tillerson on whether Washington is now committed to overthrowing Syrian President Bashar al-Assad. Trump had hinted he would be less interventionist than his predecessors and more willing to turn a blind eye to human rights abuses if it was in U.S. interests.

Italian Foreign Minister Angelino Alfano, who is hosting the meeting, said Europe's broad support for the U.S. military strikes on Syria last week has contributed to a welcomed "renewed harmony" between the United States and its partners.

Pressure on Russia likely

​British Foreign Secretary Boris Johnson said G7 foreign ministers are considering imposing new sanctions on Russian individuals over Moscow's support for the Assad government.

He said they "will be discussing the possibility of further sanctions, certainly, on some of the Syrian military figures and indeed on some of the Russian military figures."

The U.S. Ambassador to the United Nations Nikki Haley said over the weekend that regime change in Syria was a priority for Trump, while Tillerson said on Saturday the first priority was the defeat of Islamic State.

Canadian Prime Minister Justin Trudeau echoed that sentiment during a visit to Juno Beach in France on Monday. He said stability in Syria "does not involve Bashar al-Assad" and that countries that have been supportive of the regime "bear some of the responsibility" for the chemical attack.

However, there is still uncertainty over whether Washington truly wants Assad out, as many European diplomats are pushing for, or whether the missile strikes were simply a warning shot.

'It was the right thing to do,' says Canada's foreign affairs minister of Trump's Syria strikes. 8:36

The mixed messages have confused and frustrated European allies, who are eager for full U.S. support for a political solution based on a transfer of power in Damascus.

"The Americans say they agree, but there's nothing to show for it behind [the scenes]. They are absent from this and are navigating aimlessly in the dark," said a senior European diplomat, who declined to be named.

Russia was kicked out of the club of industrialized nations, formerly the G8, after its 2014 annexation of Ukraine's Crimea region and assistance for pro-Russian separatists in eastern Ukraine.

Britain's Johnson, who had been due to visit Russian counterpart Sergey Lavrov in Moscow ahead of Monday's G7 meeting, cancelled the trip at the last minute, saying the chemical attack had "changed the situation fundamentally."

He said that instead he would work with the United States and other G7 nations "to build co-ordinated international support for a cease-fire on the ground and an intensified political process."

Tillerson is due to travel to Russia after the G7 gathering, and Johnson said he will deliver a "clear and co-ordinated message to the Russians."

Trade, climate could go on backburner

The foreign ministers' discussions will prepare the way for a leaders' summit in Sicily at the end of May.

Efforts to reach an agreement on statements and strategy ahead of time — a normal part of pre-meeting G7 diplomacy — has gone very slowly, partly because of a difficult transition at the U.S. state department, where many key positions remain unfilled.

Some issues, such as trade and climate change, are likely to be ducked in Tuscany.

"The more complicated subjects will be left to the leaders," said an Italian diplomat, who declined to be named because he was not authorised to speak to the press.

However, the foreign ministers will talk about Libya.

Italy is hoping for vocal support for a United Nations-backed government in Tripoli, that has struggled to exert its influence in the city, let alone in the rest of the violence-plagued north African country.

"I have to say, the Libya experiment did not go well. We are still paying the price," Alfano said, referring to the lawlessness that has ensued since the killing of longtime dictator Moammar Gadhafi and the subsequent flow of migrants to Europe via Italy.

The Trump administration has not yet defined a clear policy and Rome fears Washington may fall into step with Egypt, which supports general Khalifa Haftar, who operates in eastern Libya.

The struggle against terrorism, relations with Iran and on-going instability in Ukraine will also come up for discussion.