Tamil dissent and stepped up the guerrilla war. By May 1985, the guerrillas were strong enough to launch an attack on Anuradhapura, attacking the Bodhi Tree shrine–a sacred site for Buddhist Sinhalese–followed by a rampage through the town. At least 150 civilians died in the hour-long attack. Rajiv Gandhi's government attempted to re-establish friendly relations with the various factions in Sri Lanka while maintaining diplomatic efforts to find a solution to the conflict as well as limiting overt aid to the Tamil militants. The Sri Lankan government, deducing a decline in support for the Tamil rebels from India, began rearming itself extensively for its anti-insurgent role with support from Pakistan, Israel, Singapore, and South Africa. In 1986, the campaign against the insurgency was stepped up. In 1987, retaliating against an increasingly bloody insurgent movement, the Vadamarachchi Operation (Operation Liberation) was launched against LTTE strongholds in Jaffna Peninsula. The operation involved nearly 10,000 troops, supported by helicopter gunships as well as ground-attack aircraft. In June 1987, the Sri Lankan Army laid siege on the town of Jaffna. This resulted in large-scale civilian casualties and created a condition of humanitarian crisis. India, which had a substantial Tamil population in South India faced the prospect of a Tamil backlash at home, called on the Sri Lankan government to halt the offensive in an attempt to negotiate a political settlement. However, the Indian efforts were unheeded. Added to this, in the growing involvement of Pakistani advisers, it was necessary for Indian interest to mount a show of force. Failing to negotiate an end to the crisis with Sri Lanka, India announced on 2 June 1987 that it wound send a convoy of unarmed ships to northern Sri Lanka to provide humanitarian assistance but this was intercepted by the Sri Lankan Navy and forced to turned back. Following the failure of the naval mission the decision was made by the Indian government to mount an airdrop of relief supplies in aid of the beleaguered civilians over the besieged city of Jaffna. On 4 June 1987, in a bid to provide relief, the Indian Air Force mounted Operation Poomalai. Five Antonov An-32s under fighter cover flew over Jaffna to airdrop 25 tons of supplies, all the time keeping well within the range of Sri Lankan radar coverage. At the same time the Sri Lankan Ambassador to New Delhi, Bernard Tilakaratna, was summoned to the Foreign Office