In a letter on Tuesday to President Kumba Yala, they said Imbali's government did not meet the conditions needed to bring about a climate of peace, stability and national reconciliation, AFP reported.
Opposition parties hold a majority of the seats in parliament.
They had already rejected Imbali's nomination during discussions with Yala ahead of the prime minister's appointment on 20 March. The material contained on this Web site comes to you via IRIN, a UN humanitarian information unit, but may not necessarily reflect the views of the United Nations or its agencies. Quotations or extracts should include attribution to the original sources. All graphics and images on this site may not be re-produced without the express permission of the original owner.