MALÉ - An explosion ripped through a speed boat carrying Maldives President Abdulla Yameen on Monday, injuring his wife and two others but leaving him unhurt.

It remains unclear what caused the explosion, which came at a time of heightened political tensions in the atoll nation after the controversial jailing of Yameen's predecessor Mohamed Nasheed.

Unconfirmed reports suggested the blast, which occurred as the tightly-guarded vessel docked in the capital island Male, came from the engine room below deck. "The first lady Fathimath Ibrahim, a senior protocol officer and a bodyguard of the president were hurt and taken to hospital," said Mohamed Hussain Shareef, minister at the President's Office. "The president was unhurt and he escorted the first lady to hospital where she is under observation following a minor injury," he told AFP.

The Maldives has launched an investigation into the incident and is seeking help from the United States and Australia to determine what happened.

Reporters had gathered at the presidential jetty to receive Yameen, who had landed a few minutes earlier at the nearby Hulhule airport after a visit to Saudi Arabia for the hajj pilgrimage.

State television footage showed the president being escorted off the boat and onto a police launch, while witnesses said they saw an ambulance rush to the jetty and authorities immediately cordoned off the area. The Maldives is a popular upmarket tourist destination, but its image has suffered in recent years due to prolonged political unrest. The country has come in for tough international criticism over the jailing of Nasheed for 13 years after conducting a rushed trial that the UN said was seriously flawed.

The charge against Nasheed relates to the ordering of the arrest of an allegedly corrupt judge when he was still president in 2012. His 13-year jail sentence was commuted to house arrest in July, but last month police took him back to prison in a surprise move that drew fresh criticism. Nasheed's international lawyer Amal Clooney has warned she will press for sanctions against the Maldives unless he is released.

That comment triggered a row with another high-profile London lawyer Cherie Booth, who is representing the government, and who said the sanctions call was "unjustified" and a threat to the economic stability of the honeymoon islands.