The United States said Saturday that Europe remains Washington's security "partner of first resort" despite a US strategic pivot to Asia, but urged Europe to pull its weight.

In a twin effort to reassure Europe about the historic US commitment to the continent, US Secretary of State Hillary Clinton and Secretary of Defence Leon Panetta delivered carefully calibrated messages of support.

Hot foreign policy issues such as Iran, Afghanistan and Syria also loomed large over the 48th annual Munich Security Conference, a gathering of world leaders, ministers and top brass.

In a speech at a roundtable talk with Panetta, Clinton pledged cooperative efforts for a united and secure Europe, mutual economic recovery, an "agile" security alliance, and a democratic Middle East along the Mediterranean.

The chief US diplomat also urged her European partners in the southern German city of Munich to work together in meeting "the opportunities that lie ahead" in the Asia-Pacific region.

"I've heard all the talk about where Europe fits into America's global outlook. I've heard some of the doubts expressed. But the reality couldn't be clearer: Europe is America's partner of first resort," she stressed.

Forced to make tough choices in tight budgetary times, the United States is shifting its military priorities to Asia and the Middle East -- even if it has pulled its troops out of Iraq and begins a drawdown in Afghanistan.

Reducing its military presence in Europe while tailoring it to future threats, Washington sees the looming strategic challenge in the Asia-Pacific as a newly powerful and assertive China rattles US allies in the region.

In opening the conference Friday, German Defence Minister Thomas de Maiziere said Europe should not fear a renewed US focus on Asia and must increasingly look after its own backyard militarily without its historic ally.

In his speech on Saturday, Panetta said: "Europe remains our security partner of choice for military operations and diplomacy around the world -- as we saw in Libya last year, and as we see in Afghanistan every day.

"We are therefore deeply committed to strengthening transatlantic security partnerships and institutions, including NATO," he said.

While the US military plans to withdraw two of its four army brigades stationed in Europe in 2014, Panetta announced that a US-based brigade will contribute to the NATO Response Force, a 13,000-strong unit created in 2002.

The US military will also rotate a battalion-sized task force to Germany to take part in exercises and training.

But Panetta also renewed pressure on European allies to keep investing in defence and to pool resources as part of the "Smart Defence" initiative aimed at maintaining military capabilities.

Polish President Bronislaw Komorowski said: "I am convinced the time is ripe for the EU to seriously take its responsibilities for the security in Europe and its neighborhood."

Meanwhile, Clinton and Germany's foreign minister Guido Westerwelle appealed for UN Security Council action to stop the bloodshed in Syria where an estimated 6,000 people have died in a 11-month crackdown on pro-democracy protesters.

"As a tyrant in Damascus brutalises his own people, America and Europe stand shoulder to shoulder. We are united, alongside the Arab League, in demanding an end to the bloodshed and a democratic future for Syria," Clinton said.

"And we are hopeful that at 10 am Eastern Standard Time in New York, the Security Council will express the will of the international community," Clinton said, referring to vote expected at 1500GMT on a UN draft resolution that condemns Damascus' action.

Clinton later met Russian Foreign Minister Sergei Lavrov on the sidelines of the Munich conference in a bid to clinch Russian support for the tough UN resolution which also supports a transition to democracy in Syria.

But Lavrov told Russian television earlier that the latest draft "does not suit us at all and I hope that it is not put to a vote."