NAKORN PATHOM, Thailand, Jan 8 (Reuters) - Tamil Tiger rebels said on Wednesday they were committed to end two decades of civil war in Sri Lanka but voiced concern that the island’s president could try to scuttle a growing peace process.

The Tigers, who wrap up a fourth round of peace talks with the government this week, also said the international situation since the September 11, 2001 attacks on the United States had added pressure on both sides to end the war.

"Both parties realise that if you continue the violence it will not lead to a solution," chief Liberation Tigers of Tamil Eelam (LTTE) negotiator Anton Balasingham told Reuters in Thailand, the venue for the talks.

"With the new international environment and the emergence of a new government committed to peace, we have decided to try and solve the problem through peaceful means," he said.

A diabetic with heart trouble, Balasingham has also had a kidney transplant and his health — his hands shook as he spoke — is a subject of concern for backers of the peace process.

"It is a terrible strain but I have to do it for my people," he said.

But Balasingham said the LTTE was worried about Sri Lanka’s political picture, with Wickremesinghe and President Chandrika Kumaratunga differing greatly on how peace should be pursued.

"Our biggest worry is the two systems of power in Colombo. The prime minister is committed to peace and the president is against the peace initiative," Balasingham said.

The two are elected separately and are fierce rivals, and while the prime minister is actively pushing the peace process, he must also work with Kumaratunga, who has vast powers including sacking parliament.

Balasingham said he hoped that by seeking a federal solution, opponents of the peace process would "realise we are seeking a solution that will not endanger the territorial integrity of Sri Lanka".

Balasingham also denied reports that the LTTE was still recruiting child soldiers, saying the practice had been stopped.

"It is true that in the past that underage people joined the movement," he said.

"We are vigorously enforcing the practice on not recruiting anyone below the age of 18 and we have also invited Amnesty International and other organisations to come and see the situation," he said.