US Secretary of State Hillary Clinton will return to work on Monday after a month-long absence caused by a series of health scares, including a blood clot in her head, the State Department said.

Clinton has been sidelined for four weeks, since she was taken ill on her return from a trip to Europe on December 7, and briefly hospitalized for a few days in New York last week.

But the State Department's schedule for the week ahead released late Sunday revealed the top diplomat will meet at 9:15 am (1415 GMT) on Monday with her assistant secretaries in Washington. The talks will be closed to the press.

A series of other meetings is planned through the week, including talks at the White House on Tuesday with Defense Secretary Leon Panetta and National Security Advisor Tom Donilon, which will also most likely not be open to TV cameras.

The high point of the week is set to be Thursday, when Clinton will host visiting Afghan President Hamid Karzai at the State Department and welcome him for a working dinner.

It has been a rare absence for the normally indefatigable Clinton, who in her four years in office has traveled almost a million miles, visited 112 countries and spent close to 400 days in a plane.

Last week, State Department spokeswoman Victoria Nuland said Clinton was "raring" to get back to work after being treated in a New York hospital for a blood clot discovered in a vein behind her right ear.

The 65-year-old diplomat was admitted to New York Presbyterian Hospital on December 30 after a scan revealed the clot in the space between her skull and her brain.

Clinton left hospital late Wednesday after three days of treatment, and headed to her home in Chappaqua, New York, as doctors who prescribed her blood thinners said they expect her to make a full recovery.

"She's looking forward to getting back to the office," Nuland said on Thursday. "She is very much planning to do so next week."

Nuland said there had been an outpouring of support for Clinton from well-wishers around the world. "I think you could call the number of goodwill messages a tsunami," she said.

It is unlikely that Clinton, the most-traveled secretary of state ever, will undertake any more foreign travel in her last weeks in the job.

Her doctors have advised her against any international trips for a while, and Clinton is due to step down towards the end of the month.

President Barack Obama has named veteran Massachusetts senator John Kerry as her successor, and he is set to sail through his confirmation hearings due later this month.

Republican Senator Lindsey Graham told CNN Sunday that he would back the Democratic Kerry to be the next secretary of state, even though he was against Obama's choice of former Republican senator Chuck Hagel to replace Panetta.

"Senator Kerry has a lot of different views than I do. We're on the opposite ends of the political spectrum, but I respect him. I think he's a thoughtful man. I think he's in the mainstream," Graham said.

Clinton first fell ill with a virulent stomach virus, which caused her to become dehydrated and faint, leading to a concussion. The blood clot is believed to have resulted from her fall.

But her illness was viewed with suspicion by her fiercest right-wing critics, who claimed she had been faking it to avoid testifying about the findings of an inquiry into the September 11 attack on a US mission in Libya.

Democratic strategist James Carville, who is a close friend of the Clintons, slammed such allegations on Friday as "inhumane, idiotic behavior."

"Hillary hating is old and deep and I guess it was still alive," he told CNN. "I was hoping after her tremendous service to the country that it would have dissipated somewhat but apparently not."

Clinton has said she still plans to testify before US lawmakers about the results of the probe into the Benghazi attack, but as yet no date has been set.

The former first lady and New York senator, has become one of the most popular figures in the Obama cabinet with approval ratings well above 60 percent.

Despite her repeated denials, many believe she is preparing to run again for the White House in 2016, after being defeated by Obama four years in her bid to be America's first woman president.