Tens of thousands of people have reportedly fled since the fighting intensified last year.

"The whole world can now see what they are doing to us. Killing and starving us to death," Elyaas, an ONLF field commander, told Al Jazeera.

The Ethiopian government denies the accusations.

"I can assure you that the government is not in the business of killing people and putting them in mass graves," Bereket Simon, a government spokesman, told the Christian Science Monitor newspaper in February.

'Greater Somalia'

The ONLF was formed in 1984, but many of its members had supported Somalia in a failed war with Ethiopia over the region in the 1970s.

The group's aims have varied over time from increased autonomy in Ethiopia to outright independence to joining a "Greater Somalia".

The Ethiopian embassy in London told Al Jazeera that the region already has a sizeable degree of autonomy and is the focus of several development initiatives.

It also said that there was no policy of refusing entry to the media.

"The ministry of foreign affairs is always ready to welcome journalists on legitimate news gathering assignments, journalists who are prepared to display the responsibility, integrity and truthfulness we would expect from employees of a newspaper," it said in a statement.

Eritrea connection

Addis Ababa says the ONLF is a terrorist organisation that it has little support among the people of the Somali region.

It also says that regional rival Eritrea is providing the separatists with assistance.

However, the ONLF rejects the claims, telling Al Jazeera that rather than being supplied by Asmara, most of their own clothes and weapons were taken from dead soldiers.

Aid agencies have said that people are suffering severe food and medical shortages in Ogaden.

"There is the possibility of a very serious humanitarian crisis in the region as a consequence of the security situation," John Holmes, the UN humanitarian chief, said.