The 12-year conflict took a deadly twist when guerrillas belonging to the Liberation Tigers of Tamil Eelam (LTTE) for the first time used surface- to-air missiles last week to down two out of the three planes that Sri Lanka's feeble air force has to ferry troops and supplies to the north.
With strategic bases at Pooneryn, Elephant Pass and Palaly now under heavy Tiger attack, Colombo officials are worried they will be unable to bring in fresh troops to stave off defeat.
The Sri Lankan bases deep inside the Tiger-held region have enough ammunition and supplies to last several weeks. But authorities claim that, as the separatist guerrillas tighten their siege, the army will be unable to evacuate its wounded soldiers.
This escalation in Sri Lanka's civil war comes after the Tigers' leader, Vilupillai Prabakharan, on 19 April broke off a 100-day ceasefire, the longest so far in this conflict, which has already claimed 34,000 lives. Many Sinhalese, who are a majority on the island, as well as the Tamils living under LTTE control on Jaffna peninsula, seemed hopeful that talks between the LTTE and envoys of the Prime Minister, Chandrika Kumaratunga, would lead to a genuine peace.
Mrs Kumaratunga was elected last year because she promised to bring peace to the island. But since the ceasefire ended, more than 230 Sri Lankan soldiers and police have been killed, and her generals are pressing her to take harsh reprisals. Not only were the two aircraft downed, but on 19 April a Tiger suicide squad of two men and two women also blew up two of the navy's eight gunboats.
Many of the Sri Lankan generals believe their criticism of Mrs Kumaratunga for being too liberal is now proving well- founded. Mr Prabakharan used the respite of the truce to plot a major offensive against the military, both in the north and the east of the island. Tamil Tigers who infiltrated during the ceasefire yesterday ambushed an lite commando patrol in the Ampara district of eastern Sri Lanka, killing 19.
Mrs Kumaratunga seems to have given up hope of a renewed ceasefire and has recently described the Tigers' leader as "a merciless megalomaniac who has killed every single person who was opposed to him".
Diplomatic sources in Colombo claim that the Sri Lankans are quietly trying to seek military aid before the Tigers overrun the northern camps.
India is seen as a possible donor, since the LTTE is held responsible for assassinating the former prime minister, Rajiv Gandhi. But India has officially denied it was approached for military assistance. An Indian "peace-keeping force" sent to Sri Lanka by Gandhi suffered heavy casualties before it withdrew in 1989, and it is doubtful that India's current Prime Minister, Narasimha Rao, facing possible elections in the autumn, would make the mistake of sacrificing Indian troops again.