Secretary of State Hillary Clinton intends to return to work this week, according to the State Department, after she was released from hospital after undergoing treatment for a blood clot on Wednesday.

"She's resting at home," State Department spokesman Victoria Nuland said on Thursday. "Some of the senior staff who spoke to her about half an hour ago say that she's sounding terrific, upbeat, raring to go."

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The 65-year-old Democrat was admitted to New York Presbyterian Hospital on Sunday after a scan revealed a clot in a vein behind her right ear in the space between her skull and her brain.

Alongside her daughter Chelsea and husband Bill, she left hospital in Manhattan late on Wednesday after three days of treatment. Doctors have prescribed her blood thinners and expect her to make a full recovery.

"She's looking forward to getting back to the office," Ms Nuland said. "She is very much planning to do so next week. And we'll have further, precise details about that as she continues to make progress."

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AFP reports Nuland said there had been an outpouring of well wishes for the former first lady.

"I think you could call the number of goodwill messages a tsunami," she said.