La Malbaie: Leaders of the Group of Seven countries have urged Russia to stop undermining democracies and say they were ready to step up sanctions against Moscow if necessary.

The leaders of the United States, Canada, Japan, France, Germany, Italy and Britain made the strongly worded statement just hours after US President Donald Trump, who is part of the G7, said he wanted Moscow re-invited to the group.

"We urge Russia to cease its destabilising behaviour, to undermine democratic systems and its support of the Syrian regime," the leaders said in a statement at the end of their two-day meeting in La Malbaie, Quebec.

The G7 leaders condemned an attack in Salisbury in Britain on a former Russian spy using a Russian-made military grade nerve agent, saying it was highly likely Moscow was responsible because there was no other plausible explanation.

Russia denies having anything to do with the attack.