The U.N.'s special envoy for Yemen says an announcement by the Houthi rebels and allies from the ousted president's party to unilaterally declare the formation of a new government in Sanaa is an obstacle to the peace process.

Former president Ali Abdullah Saleh's General People's Congress and Ansar Allah, the political arm of the Shiite rebels known as Houthis, announced the agreement Monday.

U.N. Special Envoy Ismail Ould Cheikh Ahmed said in a statement Tuesday that the announcement "does not serve the interests of the people of Yemen in these difficult times." The announcement came at a time that U.S.-backed, U.N.-mediated peace efforts have faltered.

The Houthis have been fighting forces loyal to the internationally recognized government based in Aden. The pro-government forces are backed by a Saudi-led coalition.