The United Nations and the government of Sudan are trying to secure the release of a relief plane seized by pro-government militias in the south of the country.

The Sudanese government's humanitarian aid commission said the World Food Programme aircraft has been held since last Thursday in the Fanjak region 750 km south of Khartoum with its two member crew and a UN official.

The plane was reportedly seized after three of the militia's commanders were detained by anti-government rebels and flown to southern Sudan on a UN plane.

The BBC Correspondent in Khartoum says concerns are growing in the area over the threat to humanitarian aid. The WFP is one of the few sources of relief aid to southern Sudan, which has ben affected by famine and civil war.

From the newsroom of the BBC World Service