DES MOINES, Iowa (CNN) - In an unusual move even for this dramatic and rocky presidential election season, Republican Mike Huckabee announced Monday he is pulling an ad that was scheduled to run on Iowa TV stations attacking his competitor Mitt Romney.

After making that announcement at a news conference, Huckabee showed the ad to the room full of journalists - though it took several stops and starts due to technical difficulties.

The ad is a response to Romney's latest attack ads against Huckabee. Polls show the two neck-and-neck for the lead in Iowa, which holds its caucuses Thursday.

WASHINGTON (CNN) - The woman who unsuccessfully tried to assassinate President Ford in 1975 was released on parole Monday from a federal prison in California, according to a Bureau of Prisons spokesman

 (CNN) - NASA released thousands of pages of raw data from a controversial air-safety research program Monday, but the aerospace agency's chief called the findings unreliable and left analysis up to aviation safety experts.

Surveys of more than 30,000 commercial and private pilots during the study, conducted primarily from 2001 to 2004, found extensive complaints about crew fatigue, air traffic congestion and communications. But none of the data released Monday "should be viewed or considered at this stage as having been validated," NASA Administrator Michael Griffin told reporters in a conference call Monday afternoon.

NASA had refused to release the study before its findings - including reports of twice as many bird strikes, near-mid-air collisions and runway incursions than current government monitoring systems show - leaked in October. Under criticism from Congress, Griffin agreed to release the data by year's end.

ISLAMABAD, Pakistan (CNN) - Once bitter rivals, Pakistan's two leading opposition parties are uniting in the wake of Benazir Bhutto's assassination and demanding the government not delay next week's elections as expected.

Bhutto's widower, Azif Ali Zardari, told CNN's Wolf Blitzer that he is confident the Pakistan People's Party - which he has taken control of since Bhutto's death - will be victorious in the Jan. 8 parliamentary vote.

"All the polls when she (Bhutto) was alive and all the polls in her martyrdom now have always said that Pakistan People's Party will win these elections," he said. "So we are hoping to unite the country again in a democratic form by having a win in the election."

Pakistan's Central Election Commission will meet at 9 a.m. Tuesday (11 p.m. ET Monday) and is expected to make a final decision on whether the vote will be delayed.

WASHINGTON (CNN) - The United States is warning of problems with the Kenyan election and is withholding congratulations for incumbent President Mwai Kibaki, who is claiming victory in last week's vote.

In a statement released by the U.S. State Department Monday afternoon, spokesman Tom Casey congratulated the Kenyan people for turning out in record numbers on Thursday, but added: "The United States has concerns about irregularities in reporting the results, which should be resolved promptly through constitutional and legal remedies."

He added, 'We urge all parties to restrain their supporters and reach out to each other to find a peaceful resolution in the interest of continuing to advance Kenya's democracy and development. The United States is working with all parties to this end."

–From CNN Producer Charley Keyes

(CNN) - Three Palestinians were killed and more than 10 wounded Monday in clashes between Fatah supporters and Hamas police in southern Gaza, Palestinian security and medical sources said.

Fatah supporters were celebrating the anniversary of the party's founding, despite a Hamas ban on such rallies in Gaza.

Hamas police surrounded the Fatah supporters and clashes ensued.

(CNN) - A mother and four children were killed by an allegedly intoxicated man driving his pick-up truck on the wrong side of a Toledo, Ohio, highway Sunday evening, Ohio officials say.

The near head-on crash happened shortly before 11 pm, when Michael Gagnon, 24, was driving north on the southbound side of Interstate 280 and hit a minivan carrying eight people - a mother, father, and six children or stepchildren - said Toledo Fire Department Assistant Chief Luis Santiago.

–From CNN's Sarah B. Boxer in New York

(CNN) - Mississippi Gov. Haley Barbour announced Monday that he is naming Republican Rep. Roger Wicker as Trent Lott's replacement in the Senate.

Wicker, a 13-year veteran of the House of Representatives, has a "record of getting things done for Mississippi," Barbour said.

He said one of the first requirements for a replacement was that "the appointee share Senator Lott's conservative values and views and those of Senator (Thad) Cochran's as well. Congressman Roger Wicker clearly meets that test." Cochran, Mississippi's other senator, also is a Republican, as is Lott.

(CNN) - Dutch police raided five homes in Rotterdam early Monday, arresting three men suspected of planning an imminent act of violence, according to a spokeswoman for the Netherlands' Justice Department.

Two of the suspects, ages 31 and 32, are Dutch-Moroccan and the third is a 39-year-old Sudanese man, spokeswoman Desiree Leppens told CNN.

She said special police forces conducted the raid after the Justice Department received information from General Intelligence and Security Services on the three men. "We got the information yesterday evening and around 6 o'clock (Monday morning) we had the first arrest," Leppens said.

BAGHDAD (CNN) - While 2007 has been the deadliest year for U.S. troops in Iraq, December marks the second-lowest monthly death toll of the war.

As of evening Dec. 31 in Baghdad, the U.S. government has reported 899 U.S. troops killed in Iraq in 2007. Last year the toll was 822.

The reported death toll for December stands at 21. The only lower monthly toll was 20 in February 2004.