Guinea-Bissau's government has accused Portugal of supporting an alleged coup attempt, after a deadly attack on soldiers in the capital.

The pre-dawn raid Sunday on an army barracks killed at least six people. A government spokesman says the raid was led by Captain Pansan N'tchama, an associate of army leaders who back former Prime Minister Carlos Gomes Junior.

Gomes won the first round of Guinea-Bissau's presidential election earlier this year, but the election was stopped by an April 12 military coup.

The government spokesman, Fernando Vaz, says N'tchama had recently returned from Portugal, Guinea-Bissau's former colonial power.

A Portuguese government statement Monday called for calm in Guinea-Bissau but made no mention of the accusation.

Guinea-Bissau has endured chronic unrest since winning independence in 1974.

The country has experienced numerous coups and coup attempts, most notably the assassination of President Joao Bernardo Vieria in 2009. N'tchama was allegedly involved in that killing.

The leaders of the April coup later installed a transitional government to organize new elections, winning the support of West African regional bloc ECOWAS. But the transitional government has failed to secure wider international recognition, with critics saying it remains under army influence.

The instability has made Guinea-Bissau a hub for international drug trafficking.