The US-led coalition fighting the Islamic State group was locked in a debate Tuesday over the future of its campaign in war-ravaged Syria and the fate of foreign jihadist fighters captured there.
Months of intense fighting saw US-backed forces liberate the IS stronghold of Raqa in October, leaving the group's one-time "caliphate" in tatters.
But the US fears that the jihadists could regain a foothold in the bombed-out region.
At Tuesday's meeting, "we're going to speak about the future," US Defense Secretary Jim Mattis told journalists as he travelled to Rome.
The thorny issue of what to do with the hundreds of foreign jihadists now detained in Syria will also be a key issue at the meeting in the Italian capital.
Those detainees include two Britons said to have carried out numerous beheadings.
The problem has sparked intense debate in the West about whether such fighters should be returned to their home countries to face justice.
Pentagon official Kathy Wheelbarger, accompanying Mattis, said: "We are working with the coalition on foreign fighter detainees and generally expect those detainees to return to their country of origin for disposition."
But the fate of the two Britons, Alexanda Amon Kotey and El Shafee el-Sheikh -- captured by US-backed Syrian Kurdish forces in January -- remains uncertain.
Britain's Defence Secretary Gavin Williamson told The Sun newspaper last week: "I don't think they should ever set foot in this country again."
The suspects' cell, known as "The Beatles" because of their British accents, is accused of abducting and decapitating around 20 hostages.
The victims included American journalist James Foley, who was beheaded in 2012.
The 14 defence ministers of the anti-IS coalition are also set to discuss operations in the Euphrates valley, the last refuge for fleeing jihadists in Syria.
They will also broach Turkey's controversial military offensive in the Syrian border region of Afrin against the Kurdish People's Protection Units (YPG).
The YPG has received US backing but is considered by Ankara to be a "terror group".