By Simon Gardner

COLOMBO, June 6 (Reuters) - Suspected Tamil Tiger rebels derailed a train in Sri Lanka's restive east on Wednesday with a landmine, injuring three people, the military said, a day before Japan's peace envoy was due to visit the district.

The blast in the town of Vakaneri in the eastern district of Batticaloa also came on the eve of the funeral of two slain Sri Lanka Red Cross volunteers, the latest victims in a rash of abductions and disappearances amid renewed civil war. "The blast has damaged the track. The train has gone off the track, but has not toppled," said military spokesman Prasad Samarasinghe. "It was definitely the LTTE (Liberation Tigers of Tamil Eelam)."

The Tigers were not immediately available for comment on the blast. Three passengers were injured when the train was jolted, but from falls and not shrapnel, he said.

Fighting between the state and separatist Tigers is now focused largely on the north after troops evicted the rebels from their eastern stronghold, but Batticaloa is still plagued by attacks and skirmishes.

Sri Lankan fighter jets dropped bombs near the rebels' northern stronghold on Tuesday and a suspected insurgent roadside bomb killed a police commando in Batticaloa.

JAPAN PEACE EFFORT

Yasushi Akashi, the peace envoy of Japan -- Sri Lanka's chief financial donor -- arrived on Tuesday for a five day visit to try and find ways to jumpstart a battered peace process which has descended into renewed war which has killed an estimated 4,500 people since last year alone.

Akashi is due to meet President Mahinda Rajapaksa, his brother -- the island's defence secretary -- and civil society leaders on Wednesday, and is scheduled to visit camps housing thousands of internally displaced in Batticaloa on Thursday.

Japan has played down expectations of any breakthrough from his "regular visit", but says he will seek to encourage a drive to draw up a cross-party consensus devolution proposal to end a conflict that has killed nearly 70,000 people since 1983.

Akashi's visit to the east will also coincide with the funeral of two Tamil volunteers of the Sri Lanka Red Cross, who were taken away by men who identified themselves as policemen from a train station in Colombo on Friday. Their corpses were found dumped outside the capital two days later.

United Nations Secretary-General Ban Ki-moon voiced concern for the safety of aid workers in Sri Lanka in the wake of the killings, in which the police deny any involvement.

Rajapaksa met with Red Cross officials on Tuesday and promised to bring in investigators from abroad if police failed to solve the murders within a week.

"(Rajapaksa) gave an ultimatum to the police to somehow solve this within one week and if they failed, he will get external help maybe from India or Scotland Yard," said Neville Nanayakkara, director General of the Sri Lanka Red Cross.

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