Nobody has claimed responsibility for Thursday's explosion in the capital Male that has revived security concerns in the Indian Ocean islands, known for luxury resorts but which have also faced political unrest and Islamist militant violence.

Nasheed, the Maldives' first democratically elected president who is now parliament speaker, had previously warned about militants infiltrating the country.

He was getting into his car when the blast occurred.

Local media said the explosion was caused by a device planted on a motorcycle parked near his car.

Doctors operated to remove shrapnel from Nasheed, who was now in critical condition in intensive care, ADK hospital said.

"Over the course of the past 16 hours he had life-saving surgery on injuries to his head, chest, abdomen and limbs," the hospital said in a statement.

Police Commissioner Mohamed Hameed said 450 officers had been deployed to investigate the latest incident.

"We are treating this as a terrorist attack," he told a news conference, adding that police were looking for four suspects for a possible role in the explosion.

The government is seeking technical support from foreign partners in the case.

A team from the Australian Federal Police is expected to join the investigation on Monday.

President Ibrahim Mohamed Solih, a close ally of Nasheed, said Thursday's blast was an attack on the country's democracy and its economy.

Australian Associated Press