BANDA ACEH, Jan 10: The race against time to help tsunami victims stranded in Indonesia suffered another setback Monday with the crash of a US helicopter, while separatist rebels were accused of blocking aid efforts.

Powerful aftershocks continued to rattle the badly-hit Aceh region on the northern tip of Sumatra island, where 104,000 people were killed last month and separately, key aid donor Germany hinted it would offer more debt relief.

The US navy Seahawk helicopter crashed down in a paddy field just outside Banda Aceh, the nerve centre of a huge international relief operation, shortly after 7:15am (0515 PST), injuring at least four of the 10 people on board.

The helicopter had been flying in from the aircraft carrier USS Abraham Lincoln, which has been moored off Sumatra for more than a week, dispatching a fleet of 17 helicopters on missions to deliver aid to isolated communities.

The crash, the cause of which was not yet known, was the latest in a series of hitches to blight delivery of relief to the hungry and sick along Aceh's coastal wastelands. Despite millions of dollars of aid pouring into Aceh, logistical problems have caused serious delays in distributing supplies.

The United Nations said Sunday although aid was reaching most areas of the region, some people were still without help, while the outbreak of disease remained a threat to people gathered in relief camps.

UN officials in the west Aceh town of Meulaboh, which was almost completely destroyed on Dec 26, said they were rushing in vaccinations after confirming a measles case.

Also in Meulaboh, Indonesia's military claimed separatist rebels were hampering relief efforts, posing a security risk as foreign aid workers attempted to deliver supplies.

Colonel Geerhan Lantara, army chief for west Aceh, said the country was justified in maintaining a state of emergency imposed in the region before the disaster as part of efforts to crush a decades-old rebellion. -AFP