Guinea-Bissau's military has arrested the alleged leader of a failed attack last week that the government says was an attempted counter-coup.

Captain Pansao Ntchama and at least two other suspects were detained on an island near the West African country's capital Bissau on Saturday, officials said.

The October 21 attack on elite army barracks left at least seven people dead, including six of the attackers.

Transition authorities in the country have accused its former colonial ruler Portugal of instigating the attack in a bid to reinstate former Prime Minister Carlos Gomes Junior who was ousted in an April 12 coup.

On Monday, a spokesman for Guinea-Bissau's caretaker government said Ntchama had used a vehicle belonging to a former member of Gomes Junior's government to carry out the attack.

Ntchama was the head of a commando unit believed to have assassinated President Joao Bernardo Vieira in 2009. He returned last week from Portugal where he had been undergoing military training since July 2009, security sources said.

The captain is also a former associate of the government overthrown in the April coup.

Election derailed

Tensions between Guinea-Bissau and Portugal have heightened since the military coup derailed a presidential election that Gomes Junior - now in exile in Portugal - was widely favoured to win.

The election was meant to shore up stability in the impoverished nation, which has suffered chronic instability since independence from Portugal in 1974 due to conflict between the army and state.

No president has ever completed a full term in office.

Gomes Junior was released by the military after the coup but forced to leave the country under a deal brokered by the West African regional bloc ECOWAS. He has said he hopes to return to Bissau to rule.

The caretaker government said this week it had sent an extradition request to Portugal for Gomes Junior.

A transitional administration is now ruling Guinea-Bissau with elections planned for an unspecified date in 2013.