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

Sirisena said on Friday that police chief Pujith Jayasundara had resigned but 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.

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

Jayasundara was not immediately available for comment.

The country's top defence ministry official, 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 extremists since the coordinated attacks.

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