The Philippines signed a deal with Canada on Tuesday to buy 16 combat utility helicopters worth $233.36 million, as the military prepared to step up operations against Islamist and communist rebels.

The Bell 412EPI helicopters will be delivered early next year as President Rodrigo Duterte re-focuses the armed forces modernisation programme to tackle growing domestic threats as Maoist fighters and pro-Islamic State extremists try to regroup.

"The helicopters will be used for the military's internal security operations," Major-General Restituto Padilla, military chief of plans, told Reuters, adding the aircraft could also be used for search-and-rescue and disaster relief operations.

The helicopters would replace the second-hand Vietnam War-era UH-1H Huey rotary aircraft, the workhorse of the Philippine Air Force.

The Philippines acquired those from the United States.

Defence Secretary Delfin Lorenzana signed the negotiated government contract with the Canadian Commercial Corporation, which was licensed to sell the American military aircraft.

It was the second time the Philippines has acquired Bell helicopters. In 2014, it bought eight lower variant of the aircraft for 4.8 billion pesos (about $116.6 million)

The Philippines is spending 125 billion pesos for the next five years to modernise its armed forces, but putting priority on equipment and armaments for internal security operations to defeat domestic threats as well protect its maritime borders.

It is also acquiring three frigates from South Korea, air defence radars from Israel, armoured vehicles, a long-range patrol aircraft and assault rifles and grenade launchers from Russia.