The UN food agency has warned it will stop shipments to central Somalia for 10 years if one of its ships hijacked by pirates is not returned in 48 hours.
Some 28,000 people in Somalia were displaced by the tsunami
The World Food Programme's director for the region, Robert Hauser, was speaking after reports the pirates were in talks with Somalia's interim government.
It also follows Kenyan claims that the WFP was delaying the ship's release by refusing to talk to the warlords.
The MV Semlow was taking aid to Somali victims of last December's tsunami.
It was seized on 27 June in seas between the areas of Haradheere and Hobyo, some 300 km north-east of the capital Mogadishu, as it sailed from the Kenyan port of Mombassa.
On board were 850 tonnes of rice and a crew comprising of eight Kenyans, a Tanzanian and their Sri Lankan captain, who are all reported to be safe.
But Mr Hauser told the BBC they were increasingly concerned for the safety of the ship as bad weather was bringing high winds and rough seas to Somalia's north-east coast.
In a stark warning, he said "if the food is not released within 40 hours, together with the ship and the crew, we will blacklist the area of Haradheere and Hobyo for the next 10 years."
But observers fear the WFP ultimatum will not be heeded by the pirates, and may even jeopardise the reported talks with the Somali transitional government, the BBC's Gray Phombeah in Nairobi says.
Mr Hauser rejected claims by the Kenyan government that the WFP was delaying the release of the ship and its crew by refusing to talk to the hijackers.
He said the agency was doing its best to secure their release, and stressed the WFP was grateful for Kenya's efforts in trying to resolve the matter.
Many of those affected by the tsunami rely on WFP food aid
"The problem is that the hijackers are changing their story every day. It is very difficult to know what they actually want," he said.
The hijackers initially asked for $500,000.
Mr Hauser warned that if the matter was not resolved soon, it could lead to "life-threatening situations" for the 28,000 people displaced by the Indian Ocean tsunami.
"At the moment they still have enough food from the last delivery, but very soon they will run out of that food," he said.
WFP provides an average of 3,000 tonnes of aid a month to 275,000 people in Somalia.
But its work is hampered by the fact that the country is awash with some 60,000 militia men.
Somalia has had no functioning national government since 1991.
Attempts to relocate a new transitional administration - set up in neighbouring Kenya last year - back in Somalia have so far failed.
The waters off the Somali coast are among the most dangerous in the world, the International Maritime Board says.
Earlier this month, the board warned of a surge in piracy in the region and advised vessels to stay at least 85km away from the lawless coast if possible.