European foreign ministers meeting in Brussels on Monday must increase diplomatic pressure for a ceasefire in Chad to prevent a major humanitarian crisis, British charity Oxfam said.

Some 500,000 people, including refugees from Sudan's western Darfur region and Chadians displaced by war and ethnic violence, are sheltering in camps in eastern Chad, but a surge in fighting has hampered aid and delayed the deployment of EU peacekeepers.

Many aid organisations evacuated foreign workers after a rebel assault on the Chadian capital N'Djamena two weeks ago and are operating on a skeleton staff. Oxfam said supply routes to the camps had been closed and fuel supplies for vital water plants were down to two weeks.

"We have all the elements for a huge humanitarian crisis rapidly developing in Chad," said Nick Roseveare, Oxfam's director for West Africa. "Europe must act rapidly before things get worse."

"Europe needs to call for a ceasefire in Chad to protect beleaguered civilians and increase diplomatic efforts to secure peace," he said in a statement before the Brussels meeting.

Oxfam said the camps in eastern Chad were unable to cope with a fresh wave of thousands of Darfur refugees, fleeing fresh violence.

Chadian President Idriss Deby's government, which accuses Sudan of supporting the Chadian rebels, has threatened to expel the refugees, saying their presence is destabilising the region.

Deby declared a state of emergency on Thursday, granting his government exceptional powers to censor the media, search people and property, and tightly regulate all movement around the landlocked, central African state.

European peacekeepers resumed their deployment last week, which was briefly suspended following the February 2-3 battle for N'Djamena, but the rebels have said France's strong support for Deby has made EUFOR a military target.

French troops make up the majority of the 3,700-strong force.