'The prime minister underwent coronary angiography along with a series of other tests,' K. S. Reddy told reporters at the state-owned hospital where two days of tests were conducted.

'He will be returning home tonight and will be resuming his duties from tomorrow.'

The Press Trust of India news agency, quoting unnamed hospital sources, said doctors had detected 'some blockages' in Mr Singh's cardiac vessels.

Mr Singh, 76, was advised to cancel a trip to Kolkata and undergo tests after he complained of chest pains, an official from his office said.

He has largely been in good health since he was sworn in as prime minister in May 2004 but he recently underwent surgery for a 'benign enlargement' of the prostate gland and has also had cataract treatment.

India is due to hold general elections before May. -- AFP