AN AID ship loaded with tonnes of food and medicine was preparing to sail to Jaffna last night as the UN said a humanitarian catastrophe was looming in the besieged Sri Lankan city. The vessel, flying the Red Cross flag, is expected to pick up hundreds of people, nearly all of them Tamils with foreign nationality, including around 60 British citizens who have been trapped for a week.

Electricity and telephone lines in Jaffna have been cut and food prices are spiralling as the area around the city has suffered airstrikes and bombardments in the past week. Yesterday hundreds of people were queueing outside the Red Cross offices hoping for a passage on the aid ship, but only foreign passport holders and some wounded civilians were expected to be allowed to board. The vessel’s departure has been delayed by heavy monsoon rains in Colombo, but it is expected to arrive tomorrow after a 50-hour voyage.

Jaffna is controlled by the Sri Lankan Government, but is cut off from the rest of Sri Lanka by rebel territory. The Liberation Tigers of Tamil Eelam have closed the city’s airport with artillery strikes and effectively cut sea links with the threat of suicide speedboat attacks.

Hundreds of people are thought to have been killed and about 160,000 forced from their homes by the fighting across the north and east of Sri Lanka in the past three weeks.

Jaffna is of key symbolic importance because it is the city with the biggest Tamil population and a major centre of the Tigers’ support. It has been a major battleground for more than two decades, which have left the city scarred and the people in dread of more war.

None of the British citizens trapped in Jaffna are thought to be in danger, the British High Commission in Colombo said. Most were visiting relatives when the fighting began.

• More than a dozen people have been arrested in the United States on suspicion of trying to provide money and weapons, including surface-to-air missiles, to the Tamil Tigers.

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