Health agencies were planning to launch a massive spraying campaign in Indonesia - the hardest-hit country - today to kill mosquitoes that carry the deadly disease, said Richard Allan, the director of the Mentor Initiative, the aid group leading the malaria campaign in Indonesia.
"The combination of the tsunami and the rains are creating the largest single set of [mosquito] breeding sites that Indonesia has ever seen in its history," he said.
Tsunami survivors will be highly vulnerable to the mosquito-borne illness, Mr Allan said, warning that 100,000 could die across the tsunami-hit zone.
The World Health Organisation, meanwhile, said fears the tsunami could unleash epidemics of water-based diseases, which would double the death toll, are fading as access to clean water improves.
However, relief workers in Aceh yesterday warned new rules requiring them to travel with armed escorts could cause bottlenecks in delivering aid and compromise their arm’s-length status from Indonesia’s military.
Indonesia said it was going to require that soldiers accompany foreign aid workers into Aceh province because of a threat of rebel attacks - even though a ceasefire has been declared. Aid groups said the escort requirement will hinder their work.
"We discourage such actions because it blurs the distinction between humanitarian and military efforts here," said Eileen Burke of Save the Children.
Ms Burke said her group so far has had no escorts - or problems - with its work in Sigli, about 60 miles from the provincial capital, Banda Aceh.
The rebels, who have waged a low-level war for a separate homeland for 30 years, reaffirmed their commitment to a ceasefire they declared hours after the 26 December earthquake sent killer waves across the Indian Ocean.
The death toll rose to 157,000 yesterday after Indonesia reported that 4,000 more people than was thought had died. Still, there have been unconfirmed reports of isolated skirmishes between Indonesian soldiers and rebels.
Despite the new security demands, vice-president Jusuf Kalla said the government welcomed the rebels’ declaration of a ceasefire.
"Of course we welcome it. Indonesia will also make efforts toward it," Mr Kalla said in Jakarta, the capital.
Indonesia’s moves highlight its sensitivities over foreign involvement in the humanitarian effort, especially that of foreign troops, which Indonesia has said it wants out of the country by late March.
The United Nations’ humanitarian chief, Jan Egeland, said yesterday he was worried about possible restrictions on the movement of aid workers, and stressed that it was important to save lives, not face deadlines.
He said that although roads might be cleared by the end of March, allowing civilian convoys to take over from military air operations, some military assets might still be needed throughout the aid operation.
Survivors among the tens of thousands living in refugee camps in Aceh welcomed the foreign troops, who have been flying helicopter aid missions to otherwise inaccessible areas and running field hospitals.
"If they leave, we will starve," said Syarwan, 27, a tailor who survived the tsunami and is now crowded with some 45 relatives under a tarpaulin at a survivor camp in Banda Aceh.
Others said they did not know where to go to get food.
"I see trucks passing by all the time but no-one tells us where to go if we need something," said M Jonandar, 39, whose home in Ulee Lheu, 18 miles from Banda Aceh, was destroyed.
In Sri Lanka meanwhile, UNICEF said Tamil Tiger rebels had recruited three girls - aged 11, 12 and 15 - living in tsunami refugee camps to be soldiers. The youngest two were released following an appeal for their freedom from UNICEF, said Geoffrey Keel, UNICEF spokesman in Colombo.
In southern Thailand, where nearly 5,700 were killed - half of them foreigners - Thai survivors were still trickling into refugee camps.
Pantip Ruengnat, 17, sat in a tent with relatives, cradling her six-month-old cousin, whose parents perished - two of more than 2,000 residents of Nam Khem village killed by the waves.
"We just want a house, equipment to make a living and milk for the baby," she said.
About 4,000 Thais are living in cramped conditions in the camp at Bang Muanf, which lacks basic supplies, including baby formula and tents.