By C. Bryson Hull
COLOMBO, Oct 23 (Reuters) - Anger in southern India at Sri Lanka's offensive against Tamil Tiger rebels flared on Thursday when protesters besieged a Sri Lankan diplomatic mission, the island nation's foreign ministry said.
Indian authorities also arrested V. Gopalswamy, a longtime politician better known as Vaiko, for years one of the most vocal backers of Sri Lanka's Liberation Tigers of Tamil Eelam (LTTE) separatists, police officials said.
The incidents came as anger grew in the southern Tamil Nadu state, home to the majority of the world's 77 million Tamils and epicentre of pre-election pressure on Indian Prime Minister Manmohan Singh's ruling coalition to stop Sri Lanka's war.
Sri Lanka's intensifying offensive against the LTTE, which it has fought since 1983 in one of Asia's longest insurgencies, since last week has roiled India's political scene and prompted heated diplomatic exchanges between the two neighbours.
"An unruly group had attempted to forcibly enter the premises of the Sri Lanka Deputy High Commissioner's office," Sri Lanka's Foreign Ministry said in a statement.
"In their attempt to break in, they had damaged the mission's security post."
A member of the diplomatic staff was injured by thrown stones but police stopped the protesters, it added.
India's foreign ministry had no immediate comment.
Police sources speaking on condition of anonymity said Vaiko was arrested on charges of making seditious statements, after threatening to take up arms in support of the LTTE at a rally where he accused India's government of backing Sri Lanka's army.
"We are second to none in supporting India's sovereignty but if India gives arms to Sri Lanka in name of safeguarding its sovereignty we cant keep quiet," Vaiko said before his arrest.
LTTE supporters in India say the government gives weapons to Sri Lanka, but New Delhi says it only provides non-lethal equipment. Diplomats say it also provides intelligence that has helped Sri Lanka intercept Tiger boats.
Legislators from the southern Tamil Nadu state, where the LTTE once trained and still has strong political influence, have threatened to quit the ruling party and parliament if Prime Minister Manmohan Singh does not stop the war in two weeks.
MILITARY MOMENTUM
Sri Lanka's war has presented a difficult balancing act for Singh's government, which has designated the LTTE a terrorist group but also counts Tamil politicians among its political allies. An election is due there by May.
Sri Lankan President Mahinda Rajapaksa's government is confident it can win, and has gained military and political momentum with advances deeper into rebel-held territory.
Fighting under heavy monsoon rains raged again on Thursday, and the military said it had captured the Gajabura area near the LTTE stronghold of Mullaittivu on the northeastern coast.
The LTTE could not be reached for comment. Independent verification is difficult because the government bars most journalists from the war zone.
Thursday's incidents come after India's foreign minister in a statement to parliament said Sri Lanka had assured it of the safety and rights of Tamil civilians caught up in the war.
President Rajapaksa's brother Basil, an influential adviser, is due to visit India on Sunday while his other brother Gotabhaya, the defence secretary, is due to visit Pakistan, one of Sri Lanka's major weapons suppliers.
The LTTE is on U.S., E.U. and Indian terrorism lists, and is fighting to create a separate Tamil homeland in northern Sri Lanka. Sri Lankan Tamils complain of decades of marginalisation by successive governments dominated by the Sinhalese majority.
(Additional reporting by S. Murari in Chennai and Bappa Majumdar in New Delhi; Editing by Michael Roddy)