JAKARTA: Indonesia has dispatched three warships to a maritime border area also claimed by Malaysia amid rising tensions in the Sulawesi Sea, a navy spokesman said today.

The warships were now in the disputed area off the coast of Malaysia's Sabah state and the Indonesia's East Kalimantan province, Navy Spokesman First Admiral Abdul Maliki Yusuf told AFP .

A fourth ship will leave for the area later today, Yusuf said, adding that the navy was also considering sending a submarine to the area.

"It is normal for the Indonesian navy to conduct routine patrols at its borders but following the tension there, it is imperative that we also enforce our presence and sovereignty there," Yusuf said.

Tensions had risen between the countries since Malaysia's state oil company Petronas granted energy giant Shell a concession in the area on February 16.

Formal protest

Jakarta says the area is part of its territorial waters and some of the concession granted by Malaysia overlaps with one granted by the Indonesian government to Italy's ENI and the US company Unocal in the 1960s.

Yusuf also said he has received a report that a Malaysian military plane flew over Indonesia's territory.

The Indonesian government has sent a formal protest to Malaysia over the matter but Malaysian Prime Minister Abdullah Ahmad Badawi maintains that the concession is within his country's waters.

Indonesia and Malaysia previously disputed the ownership of two small islands in the Sulawesi Sea.

But in December 2002, the International Court of Justice concluded that the islands - Ligitan and Sipadan off Borneo island - belong to Malaysia.