WASHINGTON: Sen. John Kerry has spent the past four years acting as an unofficial envoy for President Barack Obama, tamping down diplomatic fires around the globe.

Now it's official: the US Senate overwhelmingly confirmed Kerry to replace Hillary Rodham Clinton as the top American diplomat.

Tuesday's 94-3 vote to confirm Kerry as secretary of state marked his re-emergence on the world stage, eight years after he went down to defeat in his bid to unseat President George W. Bush.

Both Republicans and Democrats called Kerry the ideal successor to Clinton, who is stepping down after four years.

Kerry, 69, the son of a diplomat and a decorated Vietnam veteran, had pined for the job but was passed over in 2009. He instead became chairman of the Senate Foreign Relations Committee, and Obama tasked him with smoothing fractious ties with Afghanistan and Pakistan.

No date has been set for Kerry's swearing-in, though a welcoming ceremony is planned at the State Department on Monday.

“Sen. Kerry will need no introduction to the world's political and military leaders and will begin Day One fully conversant not only with the intricacies of US foreign policy, but able to act on a multitude of international stages,” said Sen. Bob Menendez, a Democrat who will succeed Kerry as chairman of the Foreign Relations Committee.

Sen. Bob Corker, the panel's top Republican, called Kerry “a realist” who will deal with unrest in Egypt, civil war in Syria, the threat of Al Qaeda-linked groups in Africa and Iran's pursuit of nuclear weapons.

Kerry, a forceful proponent of climate change legislation, also will have a say in whether the United States moves ahead on the Keystone XL pipeline from Canada, a divisive issue that has roiled environmentalists.

Voting against Kerry were three Republican senators – Jim Inhofe of Oklahoma, and John Cornyn and Ted Cruz, both from Texas. Two senators were absent.

“Sen. Kerry has a long history of liberal positions that are not consistent with a majority of Texans,” Cornyn said in a statement. The Texas senator is up for re-election next year and could face a conservative tea party challenge.

Kerry's smooth path to the top US diplomatic job stands in stark contrast to the harsher treatment for Obama's other national security nominees – Chuck Hagel to be defence secretary and John Brennan to be CIA director.

UN ambassador Susan Rice, believed to be Obama's top choice to head the State Department, had to withdraw her name from consideration after Republicans criticised her handling of reports on the attack on the US diplomatic mission in Benghazi, Libya, that killed Ambassador Chris Stevens and three other Americans.

Hagel, the former two-term Republican senator, faces strong opposition from some of his onetime party colleagues who question his support for reductions in the nuclear arsenal and cuts in defence spending.

Lawmakers also have questioned whether he is sufficiently supportive of Israel and strongly opposed to any outreach to Iran. Hagel has a reputation as an independent and sometimes bucked his party on some issues.

Democrats have rallied behind Hagel, and he has the announced support of at least a dozen members in advance of his confirmation hearing on Thursday.

Six Republicans have said they would vote against him, with some opposing Obama's choice even before the president's announcement.

Brennan faces questions from the Republicans about White House leaks of classified information and from Democrats about the administration's use of drones to target suspected terrorists.

Sen. Lindsey Graham, a Republican, threatened to block the nomination of both men until he gets more answers from the Obama administration about the Benghazi attack.

Graham, who earlier this month signaled he would delay Brennan's pick, said in an interview Monday night with Fox News' “On the Record” the he would “absolutely” block Hagel unless Defence Secretary Leon Panetta testifies about the Benghazi attack.

Armed Services Committee Chairman Carl Levin, a Democrat, told reporters Tuesday that a hearing with Panetta on Libya is planned though the date is uncertain.

Graham welcomed that news and said he would not thwart a committee vote on the nomination.

“Happy as a clam. News to me,” said Graham, who met with Hagel for 20 minutes on Tuesday.

Pentagon spokesman George Little said Panetta had not responded yet to the request but that the department has been forthcoming with information. He insisted that the Hagel confirmation process move as quickly as possible. As a White House emissary, Kerry has waded into hot spots around the world for Obama. He also has stepped ahead of the administration on a handful of crises.

He joined Sen. John McCain, a Republican, as an early proponent of a more aggressive policy toward Libya, pushing for using military forces to impose a “no-fly zone” over Libya as Muammar Qadhafi's forces killed rebels and other citizens.

He was one of the early voices calling for Egyptian President Hosni Mubarak to step down as revolution roiled the nation two years ago.

During his tenure, Kerry has pushed for reducing the number of nuclear weapons, shepherding a US-Russia treaty through the Senate in December 2010, and has cast climate change as a national security threat, supporting legislation that faced too many obstacles to win congressional passage.

He has led delegations to Syria and met a few times with President Bashar Assad, now a pariah in US eyes after months of civil war and bloodshed as the government looks to put down a people's rebellion. Figuring out an end-game for the Middle East country will demand all of Kerry's skills.