Manama  - Two Bahrainis have been detained as suspected terrorists and at least two others are being sought over an alleged terrorist plot which authorities said they uncovered.

A National Security Authority statement quoted an unnamed official as saying homemade explosives would have been used to disrupt National Day and Accession Day celebrations that were observed on Tuesday.

It said a group of suspects had been arrested after they allegedly planned to detonate the explosives, which contained iron pellets.

Informed sources said that the group consisted of Bahraini Shiites and that security forces had arrested at least two and were seeking two others.

Lawyer Mohammed al-Jishi told Deutsche Presse-Agentur dpa that he did not get a chance to meet the two detained, nor review details of the charges, after they appeared before the public prosecutor.

"The prosecution has ordered the two to be remanded into custody for two weeks until the investigation is completed," he said.

According to the sources, the two being sought include the brother of a Bahraini who died during the 1990s unrest, and the brother of a Bahraini who died following clashes last year.

News of the arrests came hours before arsonists set on fire an electricity sub-station on the King Faisal highway, one of the busiest streets in the capital, at a time most Shiite villages and the capital's suburbs were witnessing heavy clashes with police.

These erupted after police cordoned off a section of the city to prevent a march called for by the opposition to mark the "martyrs and victims of torture day" organized annually since unrest witnessed by the Gulf island during the early 1980s and mid 1990s.

Wednesday's clashes, which lasted into the early hours and led to the arrest of at least three people, came amid mounting tension between the opposition and the government of the Gulf kingdom, which is the only one of the six Gulf states with a Shiite majority.

The tension centers on poverty, disproportionate representation in the government, job discrimination and unemployment, and more recently allegations of large-scale naturalization of Arabs and foreigners.

Bahrain's king, Sheikh Hamad bin Isa al Khalifa, following his rise to power in 1999, introduced a package of political, economic and social reforms in 2000 as part of a national reconciliation effort.

The move, which included the release of political prisoners and the return of political exiles, for a while eased tensions - but disagreement over the newly-introduced 2002 constitution and the powers of the parliament quickly ended the calm.

Bahrain, a close US ally and home to its 5th Fleet Command, has also been struggling for the past few years with Sunni sympathizers who express support to the resistance groups in Iraq and Afghanistan. (dpa)