La Malbaie, Canada - A G7 summit dominated by disagreement over trade between the US and its key allies has failed to deliver a breakthrough as the meeting enters its second and final day.

Trump added to the disunity before his arrival at the Quebec resort town of La Malbaie on Friday when he called for Russia to be readmitted into the informal annual gathering of seven advanced economies.

The suggestion was quickly shot down by his European allies.

"Canada's position is absolutely clear. That there are no grounds whatsoever for bringing Russia with its current behaviour back into the G7," said Canadian Foreign Minister Chrystia Freeland.

Her words echoed statements from France and Germany, with German Chancellor Angela Merkel saying Russia could not be readmitted until it had made "substantial progress" on Ukraine.

Trump's suggestion was welcomed, however, by new Italian Prime Minister Giuseppe Conte, who tweeted: "Russia should re-enter the G8. It is in the interests of all."

But even Russia itself seemed to have little interest in rejoining the forum.

Kremlin spokesman Dmitry Peskov said in a statement that "Russia is focused on other formats, apart from the G7".

Russia was suspended from the G8 after it annexed Crimea from Ukraine in 2014.

The rift over Russia threatened to overshadow the more pressing concern of a brewing trade war between the US and its key allies of the past decades.

Tensions between the US and its G7 partners over trade and the US withdrawal from the Iran nuclear deal were rife in the face of the summit which had been dubbed by some as "G6 plus one", referring to an isolated US.

On May 31, the Trump administration confirmed it would apply additional tariffs on steel and aluminium imports from Canada, Mexico, and EU countries, ending a two-month exemption period.

Some countries have announced retaliatory measures against the US by introducing tariffs of their own.(FA)