MANILA, Philippines - Philippine President Rodrigo Duterte has asked Congress to extend by one year the martial law he declared in the south to ensure the "total eradication" of pro-Islamic State group extremists.

Duterte warned that extremists continue to plot public uprisings aimed at establishing a caliphate in Southeast Asia despite a failed but disastrous attempt to set up one in the southern Philippines.

Duterte said in a letter to the Senate and the House of Representatives that extending his martial law declaration in the south through the end of 2018 would allow government forces to press offensives against other armed groups, including the brutal Abu Sayyaf group and communist guerrillas, who have intensified their attacks.

A copy of the president's letter was made available to reporters Monday.