Probable next US secretary of state John Kerry called for "fresh thinking" Thursday as he outlined his foreign policy agenda and plans for relations with Iran, China and the Middle East.

"American foreign policy is not defined by drones and deployments alone," he told the Senate Foreign Relations committee, which must decide whether to not to confirm Kerry in the post of America's top diplomat.

"We cannot allow the extraordinary good that we do to save and change lives to be eclipsed entirely by the role that we have had to play since September 11th, a role that was thrust upon us," he said.

US foreign policy is also about aid, and food security, fighting disease, poverty and repression, and giving "voice to the voiceless," Kerry said.

Kerry -- a Democratic senator best known outside the United States for his unsuccessful 2004 presidential campaign -- was nominated last month by President Barack Obama to take over from Hillary Clinton.

During his almost four-hour hearing, he laid out his thoughts on some of the world's top challenges in a measured, non-confrontational way, earning praise and a warm welcome from lawmakers on both sides of the aisle.

He warned Iran the US would do "what we must" to stop it getting a nuclear weapon, told China he would work to strengthen ties and hinted he had an idea to breath fresh life into the Middle East peace process.

Kerry also vowed to be "a passionate advocate" to tackle climate change, urged the United States to build up its presence in Africa, and said Washington needed to "re-engage" with the fight against drug-trafficking in Latin America.

"I think you've acquitted yourself exceptionally well and know you're going to be confirmed in the next very few days," the top Republican member, Senator Bob Corker, said at the end of the hearing.

Sitting across from the committee which he has been a member of for 29 years, and which he has chaired since 2009, Kerry joked that he suddenly felt some sympathy for those he has grilled over the years.

Clinton, along with veteran Senator John McCain, stepped up to introduce Kerry and called him "the right choice, to carry forward the Obama administration's foreign policy."

Kerry, 69, is known to have long coveted the job, and he is expected to sail through his hearing.

But he almost lost out to US ambassador to the United Nations, Susan Rice, who had been seen as Obama's first choice until she withdrew under Republican fire over the administration's response to an attack on a US mission in Libya.

Kerry choked up when he talked of his childhood, following his diplomat father around the globe, and described "a personal journey that brought home the sacrifices and the commitment the men and women of the foreign service make every day on behalf of America."

The decorated Vietnam veteran turned anti-war activist has built impeccable credentials during his time in Senate. He has sat down with Syrian President Bashar al-Assad, soothed nerves in Pakistan and visited the Gaza Strip.

He said he felt an opportunity to steer Syria in a different direction had been lost, when Assad discussed with him the concerns of a burgeoning young population, seeking "some kind of an accommodation."

"History caught up to us. That never happened. And it's now moot because he has made a set of judgments that are inexcusable, that are reprehensible and, I think, is not long for remaining as the head of state in Syria."

Kerry also emphasized the continued need for diplomacy with Iran, but vowed there would be no policy of containment.

"The president has made it definitive -- we will do what we must to prevent Iran from obtaining a nuclear weapon," he said.

He also warned of the dangers that a two-state solution between the Israelis and Palestinians could be slipping away, saying that would be "disastrous" and hinting he may have a plan to kickstart the peace talks.

"We need to try to find a way forward, and I happen to believe that there is a way forward," said Kerry. But he refused to spell out his idea, saying: "I'm not going to say anything that prejudices our getting a negotiation going."

On China, Kerry said he wanted to pursue the administration's policy of rebalancing its policy towards an engagement with Asia "because it is critical to us to strengthen our relationship in China."

And while there were tensions and disagreements, he said "we make progress. It's incremental... It's a tough slog."

He also vowed to maintain some of the programs championed by Clinton such as the State Department's emphasis on women's rights around the world.