Pressing security threats from jihadist groups across the world and "Russian aggression" in Ukraine dominated world leaders' talks Monday at the second day of the G7 summit in Germany.

Barring Russian President Vladimir Putin for a third time, the Group of Seven leaders invited others beyond the club of rich nations, including Iraq's premier and Nigeria's president, both battling deadly Islamist violence.

Iraq's Prime Minister Haider al-Abadi was scheduled to discuss the US-led campaign to help his country fight the Islamic State extremists who launched a lightning offensive a year ago and have snatched over a third of the country's territory.

Abadi will also get one-on-one time with Obama to discuss the Washington-led campaign to help Baghdad recover territory lost to IS militants, whose self-proclaimed "caliphate" extends deep into neighbouring Syria.

The power summit, held in a tightly-secured resort in the picture-postcard Bavarian Alps, was also expected to hold talks on "foreign fighters" and the threat Islamist extremism poses to their countries -- Britain, Canada, France, Germany, Italy, Japan and the United States.

Another visitor to the summit, Nigeria's newly elected President Muhammadu Buhari, was to put a "shopping list" to the G7 leaders, seeking help to fight an insurgency by Boko Haram Islamists blamed for 15,000 deaths since 2009.

Buhari has been tested with 11 separate attacks that have left at least 93 dead in the week he has been in the job.

- Sanctions against Russia -

The first day of the G7 was dominated by the Ukraine conflict, as Obama and the summit host, Chancellor Angela Merkel, urged the global community to stand firm against Moscow until it complies with a Ukraine ceasefire deal struck in the Belarussian capital Minsk.

"I expect that we should send a firm signal here. Not sanctions as an end to itself, but sanctions... to reach a target," Merkel told ZDF television.

Japan's Prime Minister Shinzo Abe and Canada's Stephen Harper on Saturday made a point of visiting Kiev on their way to the summit, to voice support for Ukraine's embattled leaders, as a recent flare-up in fighting in the east has left at least 28 dead.

Although Putin has insisted that "there's no need to be afraid of Russia", the latest escalation has sparked fears that the hard-won ceasefire brokered by France and Germany four months ago could be derailed.

Another pressing problem has been the haggling between debt-hit Greece and its international creditors -- the EU, ECB and IMF -- and the fear that a messy default could lead to Greece exiting the eurozone, with unknown repercussions for the world economy.

The issue was expected to arise again when the G7 leaders meet another guest in their "outreach talks" Monday, International Monetary Fund chief Christine Lagarde.

On Sunday, European Commission President Jean-Claude Juncker hit out at Greece's Prime Minister Alexis Tspiras saying he has misrepresented the EU's offer to Athens.

And confusion broke out Monday when a French official told reporters Obama had complained about the strength of the dollar -- comments swiftly quashed by a US official.

- Climate change, China's ambitions -

Merkel and French President Francois Hollande, meanwhile, were expected to seek consensus with G7 counterparts on another burning global issue, climate change, ahead of a crunch year-end United Nations summit in Paris.

The aim is to send a clear signal to push other nations taking part in the Paris meeting to commit to reducing dangerous greenhouse gas emissions, which threaten to melt ice caps and glaciers, raise sea levels and bring more violent storms and floods.

"Commitments have to be made at the G7. At the moment, the communique is going in the right direction," said Hollande before the second day of talks.

He said he would be pushing for "realistic and objective" commitments to reduce global warming in the coming years.

Abe was expected to draw attention to a pressing regional issue -- China's assertions over most of the disputed South China Sea, where its territorial claims clash with those of several other nations.

Alarm is growing in Asia over the issue and the United States has said China's actions were "out of step" with international norms.

Citing unnamed sources, Japan's Yomiuri newspaper said the G7 would in their joint statement express concern about unilateral attempts to change the status quo in the South China Sea, while no country would be named in the communique.

As has become tradition at such gathering, several thousand anti-G7 protesters marched over the weekend in largely peaceful demonstrations.

There were a handful of clashes with the police and a few arrests but overall the demonstrations were colourful and non-violent.