US President Barack Obama and Vladimir Putin of Russia agreed Sunday on the first steps towards peace in Syria, as the Paris attacks jolted world leaders into a crackdown on foreign fighters.

The horror of the attacks in Paris shook leaders at a summit in Turkey, adding a new urgency to their search for a solution to the four-year war in Syria that has enabled the rise of Islamic State jihadists.

Putting aside important differences, Obama and Putin met over a coffee table on the sidelines of the Group of 20 summit in the resort of Antalya to align their positions on Syria after the Paris assaults, which killed at least 129 people and were claimed by IS.

"The conversation lasted approximately 35 minutes and centred around ongoing efforts to resolve the conflict in Syria, an imperative made all the more urgent by the horrifying terrorist attacks in Paris," a US official said.

Obama and Putin agreed on the need for United Nations talks, a ceasefire and a transition government in Syria, the US official said, echoing a plan for Syria already forged by diplomats at talks in Vienna the previous day.

The Kremlin said "divergences" remained on tactics even if they shared the same goal against Islamic State.

It was the two presidents' first meeting since Russia in September launched an air campaign in Syria which the Kremlin insists is aimed against IS jihadists. The West however suspects Moscow's true aim is to target opponents of Syrian President Bashar al-Assad.

In images captured on Turkish public television, Putin and Obama were seen hunching towards each other as they held animated talks, in stark contrast to the frigid body language that marked previous meetings.

- 'Destroy death cult' -

The Paris attacks on Friday darkened the mood and injected urgency into anti-terrorism discussions at the G20 summit, which is also grappling with the spreading refugee crisis, climate change and tax avoidance by multinational corporations.

Host President Recep Tayyip Erdogan declared a minute of silence for the Paris victims before the plenary session got under way.

In a draft special statement obtained by AFP a day before its formal adoption, world leaders raised the alarm over an "acute and growing flow of foreign terrorist fighters".

They vowed to share intelligence, track border crossings and boost aviation security to halt the movement of jihadist fighters.

British Prime Minister David Cameron said security in Europe depended on destroying the "death cult" of IS in its strongholds of northern Iraq and Syria.

"We need to keep on making the case that we will be safer in the UK, in France and across Europe if we destroy this death cult once and for all," said Cameron.

Chinese President Xi Jinping said terrorism is a "common enemy" and called for "a joint front to fight against" the threat.

- 'Turkey foils attack' -

Turkey also said it had foiled an Islamic State plot to launch a major attack in its biggest city Istanbul on Friday, the same day as the Paris attacks.

An official told AFP that the security forces had arrested a gang of five extremists, including an associate of the notorious British Islamic State executioner Mohammed Emwazi, widely known as "Jihadi John".

The migrant crisis is a key topic at the G20 summit, with Turkey housing some 2.2 million Syrian refugees but the European Union is urging Ankara to do more to prevent migrants undertaking risky boat crossings to reach the EU.

With some eastern European members expressing concern about accepting more refugees, European Commission head Jean-Claude Juncker warned that the attacks in Paris should in no way poison the sensitive debate over refugees.

"Those who organised, who perpetrated the attacks are the very same people who the refugees are fleeing and not the opposite," Juncker said.

Discussions on climate change will assume greater importance than usual coming ahead of a UN climate conference in Paris at the end of the month that aims to agree a global pact to curb warming of the planet.

French Foreign Minister Laurent Fabius urged leaders to strengthen a planned G20 declaration on global warming, sources said.

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Cameron International