US Navy medical experts have arrived in Sudan to help analyse samples of suspected yellow fever, which has killed 127 people in the Darfur region since early September, health officials said on Friday.

The arrival of Cairo-based US Naval Medical Research Unit 3 (NAMRU-3) comes as a vaccination campaign against the rare outbreak intensifies.

NAMRU-3 will "support laboratory analysis of collected samples as well as conduct on-job training sessions at the National Public Health Laboratory starting on Saturday", said a joint statement from the UN's World Health Organisation and Sudan's health ministry.

The US embassy spokesman could not be immediately reached.

NAMRU-3 monitors disease threats of military and public health importance and develops strategies against them, working with WHO and other organisations, the US agency's website says.

The naval unit already has a research partnership with Sudan, along with other countries in the region, the website says.

Cooperation between the US experts and Sudan comes despite Washington's 15-year-old trade sanctions imposed on Khartoum over human rights and other concerns.

Health officials have recorded 537 suspected yellow fever cases, including 127 deaths, since September 2 in Darfur.

A campaign to vaccinate more than two million people against the mosquito-born virus began on Tuesday.

Sudan's impoverished western Darfur region has been plagued by conflict since ethnic minority rebels rose against the Arab-dominated Khartoum government in 2003.