BAGHDAD, Iraq — Campaigning around Iraq stopped today to give the country's 15 million voters an opportunity to reflect before deciding who will govern their country for the next four years.

Streets in Baghdad were eerily quiet the day before Thursday's election, with police strictly enforcing a traffic ban. Only the noise from an occasional siren, sporadic gunshot or a U.S. helicopter overhead could be heard. Borders and airports have also been closed and the nighttime curfew has been extended in an effort to secure the vote.

Two police officers were killed and four others were injured by a roadside bomb that exploded next to an Interior Ministry patrol in northern Mosul, the city's al-Jumhouri hospital said.

Iraq's election commission said it had registered 6,655 candidates running on 996 lists and had certified 307 political groups — either in the form of single candidates or parties — and 19 coalitions.

Baghdad is the biggest electoral district with 2,161 candidates running for 59 of the 275 seats in parliament, said the commission's executive director, Adel Ali al-Lami. There are 33,000 polling stations around the country.

The Interior Ministry, meanwhile, denied reports that a tanker truck filled with thousands of blank ballots had been confiscated near the Iranian border. Earlier in the day, a security official speaking on condition of anonymity because he was not authorized to talk to the media, said a truck had been seized in the border town of Badra.

On the last day of campaigning Tuesday, a roadside bomb killed four American soldiers and gunmen assassinated a candidate for parliament. The American deaths in Baghdad brought to at least 2,149 the number of U.S. service members who have died since the start of the war in 2003, according to an Associated Press count.