A top Japanese peace envoy arrived in Sri Lanka Tuesday as Sri Lanka's military jets pounded rebel positions in the island's north.

Yasushi Akashi is visiting Sri Lanka this week from Japan, the single largest donor to Sri Lanka, in an effort to revive the nation's shattered peace process.

A 2002 ceasefire has been routinely violated by both the Sri Lankan government and the rebel Tamil Tigers. An estimated 4,000 people have been killed during the past 18 months.

Defense officials Tuesday said Sri Lankan war planes bombed rebel positions in the northern area of Mankulam. In the past few days, the military has targeted nearby Vavuniya with aerial air strikes and clashed with rebels there.

The military also says a roadside bomb planted by suspected Tamil rebels exploded Tuesday in eastern Batticaloa, killing a police officer.

Also today, United Nations Secretary-General Ban Ki-moon expressed concern for the safety of aid workers in Sri Lanka, just days after two Red Cross workers were abducted and murdered. In a statement, he reminded combatants that aid workers have a right to protection at all times.

Tamil rebels have been fighting for independence in the northern and eastern areas of Sri Lanka since 1983. They argue ethnic Tamils have been oppressed by the nation's Sinhalese majority.

Some information for this report was provided by AFP and Reuters.