Turkey attack highlights dangers on Clinton's last day

US Secretary of State Hillary Clinton was to bid a final farewell to her staff Friday, but her last day was marred by the latest in a series of attacks on American missions in the Muslim world.

Just hours after Clinton warned in her last public address "it is hard to predict what any day in this job will bring," a suicide bomber blew himself up at the US embassy in Ankara.

US officials said they were probing what happened in the attack, believed to have been carried out by a militant from an outlawed leftwing group, in which a Turkish security guard was killed and several other people wounded.

"We can confirm a terrorist blast at a checkpoint on the perimeter of our embassy compound in Ankara, Turkey at 1:13pm local time," State Department spokeswoman Victoria Nuland said.

"We are working closely with the Turkish national police to make a full assessment of the damage and the casualties, and to begin an investigation," she added in a statement issued just over two hours after the attack.

The bombing once again exposes the vulnerability of the army of 70,000 US diplomats -- many of whom operate in the world's hotspots -- an issue set to be one of the top priorities for incoming secretary of state John Kerry.

It also came almost five months after heavily-armed militants stormed the US mission in Benghazi, eastern Libya, killing the ambassador and three more Americans.

And it came just two weeks after three Americans were among 38 foreigners killed in a hostage-taking in Algeria.

The Benghazi assault unleashed a political firestorm, with the Obama administration coming under Republican fire, accused of trying to cover up the true sequence of events and dropping the ball on security at the mission.

Kerry, who was to be sworn in at a private ceremony by Justice Elena Kagan later Friday, told the Boston Globe that he would begin working on diplomatic protection when he starts work at 9:00 am (1300 GMT) Monday.

"There are certain things I intend to issue instructions on the minute I come in," Kerry told the leading daily paper in his home state of Massachusetts, where he served as a senator for 28 years.

"I won't go into the details, but Benghazi, embassy security, issues regarding some of the analysis that I want to track with respect to Iran, with respect to Syria. Trouble spots."

Kerry also pointed to a "major meeting on Syria in the next few days."

Clinton was set to leave the State Department through its marble-columned entrance at around 1930 GMT Friday, with hundreds of staff expected to gather to wave her off.

She is stepping down with record popularity ratings of around 65 percent, and amid intense speculation that she could launch a second bid to be the nation's first woman president in the 2016 elections.

Clinton, the former first lady and New York senator, has so far said she doesn't see herself returning to politics, saying instead she wants to work on advocacy and philanthropy and continue "the cause of my life," furthering the rights of women and girls.

But political analysts say she could be the Democratic Party's best hope in four more years, and she would have good odds of breaking through that last glass ceiling, after President Barack Obama defeated her in the 2008 primaries.

"She is (a) more admired, less polarizing figure than she was in 2008," Democratic strategist Geoff Garin, who has worked for Clinton in the past, told National Public Radio.

"The political prospects are really quite good, and better than they were when she last ran for president."

Kerry meanwhile revealed he would make his first foreign trip in February, but said he had no plans to beat Clinton's record of visiting 112 countries.

He also said Obama had asked him to replace Clinton a full week before US ambassador to the United Nations, Susan Rice, pulled out of the race.

Rice, who had been thought to be Obama's first choice for the post, had come under Republican fire for comments she made during the Benghazi maelstrom.