The top U.N. humanitarian official says she received a letter from a rebel group in Sudan proposing a halt in hostilities to allow access to civilians in need.

Valerie Amos says the Sudan Revolutionary Front wrote to her last week to indicate its willingness to work with the United Nations and the African Union to negotiate a "temporary cessation of hostilities" to help humanitarian workers reach civilians. She said the U.N. would "actively follow up on that offer."

The front is an alliance of two rebel groups fighting Sudan's government: The SPLM-North, a group ideologically aligned with independent South Sudan, and the Justice and Equality Movement, which is fighting in Sudan's troubled western region of Darfur.

Amos said there are 4.4 million people in need of assistance in Sudan.