The Group of Seven leading democracies began the concluding day of their annual summit in discussions with leaders from Ethiopia, Kenya, Niger, Nigeria, and Tunisia.

The five African states are key players in the Mediterranean migration crisis, as countries of origin or transit for hundreds of thousands of migrants attempting to reach Europe via perilous crossings of the Mediterranean. The G7's Italian presidency placed this year's summit in Sicily to underline the proximity of the crisis.

But even that has prompted discord among the summiteers as Trump, according to Italian sources, resists the hosts' desire to issue a declaration underlining the benefits as well as pitfalls of migration.

That sort of language is anathema to a White House that wants to impose a ban on travellers from six Muslim-majority countries.

After starting his first presidential trip abroad wreathed in smiles, Trump is ending it with rebukes, upbraiding America's European partners over military spending, trade and global warming.

An enduring motif of the G7, which represents the lion's share of global economic output, has been to champion free trade.

At last year's summit in Japan, it issued a lengthy communique in support of resisting protectionism, as well as helping refugees and fighting climate change.

But that was then, when Barack Obama still occupied the White House. Today, his successor is defiant about stepping out of the G7 line.

"His basis for decision ultimately will be what's best for the United States," top economic advisor Gary Cohn said at the annual talks in Sicily's ancient hilltop resort of Taormina.

Cohn was referring to whether Trump will execute his threat to walk away from the Paris accord on combatting climate change.

But his language also summarises the "America First" platform that elevated the property tycoon to victory in last year's presidential election.