US Senator Ted Kennedy has been hospitalised with symptoms of a stroke.
Mr Kennedy, 76, was taken to the hospital in Cape Cod, Massachusetts, early this morning.
The long-serving Massachusetts senator is a leading liberal voice in the US who has actively campaigned for Barack Obama in his bid for the Democratic presidential nomination.
Kennedy had preventive surgery in Boston in October to unclog a partially blocked carotid artery in his neck.
The blockage was discovered during a routine check of Kennedy's back and spine, doctors said. A blocked carotid artery can lead to a stroke and death, they said.
Ted Kennedy has suffered from back problems since a plane crash in 1964 in which the pilot and one of Kennedy's aides were killed .
The senator was pulled from the wreckage with a back injury, punctured lung, broken ribs and internal bleeding.
The youngest brother of assassinated US President John F Kennedy, Ted Kennedy was elected to the Senate in 1962 and currently serves as chairman of the Senate Committee on Health, Education, Labor and Pensions.
He helped win an increase in the national minimum wage this year and worked with Republicans to produce broad immigration reform, which failed in the Senate after stiff opposition from conservative Republicans.
