BAGHDAD, Iraq — Sunni Arab and secular groups refused today to open discussions with the Shiite religious bloc leading in Iraq's parliamentary elections until a full review of the contested results is carried out.

Their refusal could deepen the political turmoil following a U.N. observer's endorsement of Iraq's Dec. 15 elections. The official said the results were credible and that the results should stand.

"We are not taking part in discussions," said Nasser al-Ani, a senior official in the main Sunni Arab coalition — the Iraqi Accordance Front.

Preliminary results from the vote have given the governing Shiite religious bloc, the United Iraqi Alliance, a big lead — but one which still would require forming a coalition with other groups. Al-Ani told The Associated Press that his political group favored participating in a broad-based coalition government, but would not begin contacts "until we get a clear picture about the results of the investigation."

The U.N. endorsement came on Wednesday after opposition groups demanded international intervention and an independent review of more than 1,500 complaints about irregularities.

Al-Hakim has said that preparations were being made to choose a candidate for prime minister, who they have said must come from the United Iraqi Alliance.

Alliance officials have indicated likely candidates are current Prime Minister Ibrahim al-Jaafari, who heads the Islamic Dawa party, and Adel Abdul-Mahdi, who belongs to the other main Shiite party, the Supreme Council of the Islamic Revolution in Iraq.

In violence today, a suicide bomber detonated his explosives belt on a street near the Interior Ministry, killing one police officer and wounding four, police said. Earlier police had said four were killed. Gunmen in Baghdad assassinated an Iraqi driver working with a French company, police Capt. Qassem Hussein said, adding that a university student in northwestern Baghdad was killed in a drive-by shooting.