Guinea-Bissau's interim government has convened a crisis meeting with security chiefs, after former president Kumba Yalla declared himself head of state Sunday. Mr. Yalla was ousted in a bloodless coup two-years ago. He is scheduled to run as a presidential candidate in June elections.

Security was tightened around the presidential palace in Guinea-Bissau's capital, Bissau, after Kumba Yalla unilaterally declared himself president.

Defense Minister Martinho Ndafa Cadi said, after a meeting convened by the interim president, that although the government was not pre-occupied by Mr. Yalla's declarations, it remained watchful.

General Bitchofla Na Fase, who led the military coup against Mr. Yalla, said he remained loyal to the interim civilian leader Henrique Rosa.

Wearing his characteristic red hat, Mr. Yalla told journalists and supporters at his home Sunday that he had been forced to sign a letter renouncing the presidency in 2003. He said would now serve out the remaining 18 months that were left of his presidential term in office. He added that presidential polls scheduled for June may be delayed.

An analyst for the London-based research group Global Securities, Chris Melville, says Mr. Yalla has the support of some senior army officers and soldiers who belong to his majority Balante ethnic group. Mr. Melville says a coup in favour of Mr. Yalla is still possible.

Mr. Melville says that although Mr. Yalla's presidency was characterized by mismanagement and corruption, he still enjoys popular support amongst the majority Balante ethnic group.

But he says it is difficult to say what effect Mr. Yalla's unilateral declaration will have.

"Whether or not that popular support would extend to him effectively overriding the democratic process, by unilaterally announcing his presidency, and demanding the postponement or cancellation of the polls, I am not sure," he said. "I mean it might actually undermine any legitimacy that he has within his core support group."

But Mr. Melville adds that given Mr. Yalla's record, the comment was not surprising.

"His term in office between 2001 and 2003 was characterized by this eccentricity and irresponsibility, and it is entirely consistent with his character that he should act in this way again," he said.

U.N. Secretary-General Kofi Annan says he is deeply concerned by Mr. Yalla's statement, which was apparently trying to disrupt the ongoing transitional process to restore democracy to the former Portuguese colony.

Guinea Bissau's Supreme Court made a controversial decision recently, to allow Mr. Yalla to run in June's presidential elections. Mr. Yalla was banned from participating in politics for five years, but is seen as a frontrunner in election polls.

The Supreme Court has also allowed former 1990s military ruler Joao Bernardo Vieira, who was also ousted in a coup, to run.

It is widely hoped that elections will restore stability in the small West African state that has had a repeated history of coups,