US Secretary of State Rex Tillerson has used a visit to a Second World War memorial in Italy to declare that the United States will stand up to aggressors who harm civilians.
It came as the Trump administration sought to rally world leaders behind a strategy to resolve Syria's protracted civil war.
Opening his visit to Italy, Mr Tillerson travelled up a winding mountain road to Sant'Anna di Stazzema, the Tuscan village where the Nazis massacred more than 500 civilians during the Second World War.
As he laid a wreath at the site, he alluded to the chemical attack in Syria last week that triggered retaliatory US air strikes.
"We rededicate ourselves to holding to account any and all who commit crimes against the innocents anywhere in the world," Mr Tillerson said.
"This place will serve as an inspiration to us all."
Mr Tillerson's visit to Europe has been overshadowed from the start by President Donald Trump's decision to punish Syrian President Bashar Assad for using chemical weapons by launching cruise missiles at a Syrian air base.
The US military action has renewed the world's focus on Mr Assad's fate and on Syria's civil war, now in its seventh year.
The secretary of state's pledge to stand up for innocents came as Mr Assad has continued to attack civilians in Syria in the days since the US air strikes - including in the part of Idlib province where the chemical attack occurred.
And while other US air strikes in Syria have targeted the Islamic State group, the US has acknowledged that civilian casualties sometimes occur.
Mr Tillerson plans to use his meetings with foreign ministers from the Group of 7 industrialised economies - normally a venue for economic discussions - to try to persuade leading countries to support the US plan.
The centrepiece of that diplomacy will come on Tuesday morning when Mr Tillerson takes part in a meeting of "like-minded" nations on Syria, including several Arab nations invited to attend.
The top American diplomat began to deliver that message on Monday when he met on the sidelines of the G7 with British Foreign Secretary Boris Johnson and French Foreign Minister Jean-Marc Ayrault.
Both countries have voiced support for the US response to Mr Assad's chemical weapons use.
The Trump administration is hoping that after defeating IS in Syria, it can restore stability by securing local cease-fires between Mr Assad's government and opposition groups that allow local leaders who have fled to return and by restoring basic services.
The next step would be to use UN talks to negotiate a political transition that could include Mr Assad leaving power.
From Italy, Mr Tillerson will travel to Moscow, becoming the first Trump administration official to visit Russia.
That trip, too, is fraught with tension over Syria:
Mr Tillerson has blamed Russia, Mr Assad's strongest ally, of either complicity or incompetence for allowing Mr Assad to possess and use chemical weapons.