COLOMBO (AFP) - Sri Lanka's incumbent police chief has refused to step down over the Easter Sunday suicide attacks despite President Maithripala Sirisena on Monday (April 29) naming his successor.

Mr Sirisena said last Friday that police chief Pujith Jayasundara had resigned, but Mr Jayasundara never sent the letter, officials said, and has remained in his government residence.

The President has now named Deputy Inspector-General Chandana Wickramaratne as acting police chief, an official involved in the process said.

Mr Sirisena had accused Mr Jayasundara of failing to act on intelligence reports warning that suicide bombers were likely to target churches.

The April 21 Easter Sunday attacks left 253 dead and a major political row has ensued.

"Jayasundara has defied the president and stayed on," the official said.

"This means Jayasundara is effectively suspended, pending his formal removal through an impeachment motion in Parliament."

Mr Jayasundara was not immediately available for comment.

The country's top defence ministry official, Mr Hemasiri Fernando, resigned last week after he too was told by the President to step down over the security failure.

The government has declared a state of emergency and deployed thousands of troops for search operations against Islamist extremists since the coordinated attacks.

Over 150 people have been arrested since April 21 and more than 15 people killed in raids.