Heavy rains pelted homeless cyclone survivors in Burma's Irrawaddy delta on Tuesday, complicating already slow delivery of aid to more than 1.5 million people facing hunger and disease. As more foreign aid trickled into the former Burma, critics ratcheted up the pressure on its military rulers to accelerate a relief effort that is only delivering an estimated one-tenth of the supplies needed in the devastated delta. "The response of the regime in Burma to this crisis has been absolutely callous and those paying the price of this callousness have been the long-suffering Burmese people," Australian Prime Minister Kevin Rudd told Parliament. An Australian air force plane landed in Rangoon, Burma's main city, with 31 tonnes of emergency supplies, a day after the first US military aid flight arrived in a country Washington has described as an "outpost of tyranny". Two more US flights were due on Tuesday as part of a "confidence building" effort to prod Burma's reclusive generals into allowing a larger international relief operation 11 days after the disaster left up to 100,000 dead or missing. Tens of thousands of people throughout the delta are crammed into monasteries, schools and other buildings after arriving in towns that were on the breadline even before the disaster. Lacking food, water and sanitation, they face the threat of killer diseases such as cholera. Heavy rains added to the misery of survivors with little shelter. "Where I am now there's over 10,000 homeless people and it's pouring rain," Bridget Gardener of the International Red Cross said during a rare tour of the delta by a foreign aid official.