The U.S. ambassador to Iraq (search) acknowledged serious problems ahead of next weekend's election but gave assurance Sunday that "great efforts" were being made so every Iraqi can vote. In an audiotape posted on the Web, a speaker claiming to be Iraq's most feared terrorist declared "fierce war" on democracy, raising the stakes in the vote.

Rebels who have vowed to disrupt the balloting blew up a designated polling station near Hillah (search) south of Baghdad and stormed a police station in Ramadi west of the capital, authorities said.

A U.S. soldier was killed Saturday on a security patrol in the northern city of Mosul, the military said Sunday. Large explosions and heavy gunfire also were heard in eastern Mosul late Sunday.

Three U.S. soldiers were wounded Sunday in a mortar attack in Samarra north of Baghdad, the U.S. command said. One of the soldiers was being evacuated to a U.S. military hospital in Germany with serious injuries.

U.S. and Iraqi officials fear more such attacks in the run-up to the Jan. 30 election and have announced massive security measures to protect voters. Iraqis will choose a 275-seat National Assembly and provincial councils in Iraq's 18 provinces in the first nationwide balloting since the ouster of Saddam Hussein (search) in 2003.

Large turnouts are expected among Iraq's majority Shiite Muslims in the south and minority Kurds in the northeast. But the big question is whether Sunni Arabs, who form the core of the insurgency, will defy rebel threats and their clergy's calls for a boycott and participate in substantial numbers.

Failure of significant numbers of Sunnis to participate would call into question the legitimacy of the new Iraqi leadership, widening the gulf among the country's ethnic and religious groups and setting the stage for even more turmoil.

"The Iraqis will be — will be just fine," Secretary of State nominee Condoleezza Rice told reporters Sunday at the White House. "They're starting a process and this is an important step, a first step for them in this democratic process."

In a series of interviews Sunday on American television talk shows, U.S. Ambassador John Negroponte acknowledged an increase in rebel intimidation of Iraqi officials and security forces and said serious security problems remain in the Sunni Triangle north and west of Baghdad.

"But security measures are being taken, by both the multinational forces here in Iraq as well as the Iraqi armed forces and police," Negroponte told "Fox News Sunday."

"There will be some problematic areas ... But even there, great efforts are being made to enable every Iraqi eligible to do so to be able to vote," he said.

Underscoring the threat, a speaker identifying himself as Abu Musab al-Zarqawi — the leader of Iraq's Al Qaeda affiliate — condemned the election, branding candidates as "demi-idols" and saying those who vote for them "are infidels" — a clear threat to the safety of all those who participate in the balloting.

"We have declared a fierce war on this evil principle of democracy and those who follow this wrong ideology," the speaker said in an audiotape posted Sunday on an Islamic Web site. "Anyone who tries to help set up this system is part of it."

The speaker warned Iraqis to be careful of "the enemy's plan to implement so-called democracy in your country." He said the Americans have engineered the election to install Shiite Muslims in power. Al-Zarqawi has in the past branded Shiites as heretics.

The United States has offered a $25 million reward for al-Zarqawi's capture or death — the same amount as for Al Qaeda leader Usama bin Laden.

Most of the insurgents are believed to be Sunni Arabs, who lost influence and privilege with the fall of their patron Saddam. Their ranks have been reinforced by non-Iraqi Arab extremists who have come to wage holy war against the Americans.

To encourage as big a turnout of Sunnis as possible, U.S. and Iraqi troops have stepped up security operations in Baghdad, Mosul and other tense areas, rounding up hundreds of suspected insurgents. The U.S. command announced Sunday it had arrested an undisclosed "top insurgent suspect" in Baghdad after hunting him for nearly a year.

Sunni elder statesman Adnan Pachachi, who is running for the National Assembly, predicted a bigger Sunni turnout than expected due to recent improvements in the security situation in some areas.

"There is evidence that participation in the elections will be broader than expected," Pachachi told Al-Arabiya television. "I call on the parties that planned to boycott the elections to urge their followers to vote."

He also said in another televised interview that it was important to maintain adequate Sunni representation in the new assembly.

In order to shake public confidence in the elections, insurgents have accelerated attacks against Iraq's security services, trained by the Americans but plagued by leadership and morale problems.

A major insurgent group, the Ansar al-Sunnah Army, posted a videotape Sunday on a Web site showing the assassination of an Iraqi army colonel captured in Mosul. The tape showed a man in civilian clothes holding a military identification card. As the man sat in a chair, a masked gunman approached from his right and shot him in the head with a rifle.

Another video posted on the Internet Sunday purportedly showed the shooting death of a captive Egyptian truck driver.

The hostage, seated in front of the trademark flag of al-Zarqawi's group, identified himself as Ibrahim Mohammed Ismail and warned foreign drivers not to work in Iraq.

Ismail said he was taken captive when his trailer truck broke down while he was transporting supplies to Ramadi from Safwan, on the Kuwaiti border.

The video then moved outside, showing Ismail, 39, blindfolded and his hands tied behind his back. A masked gunman shot him with three rounds in the back in daylight on a street corner as traffic passed by.

The authenticity of the video could not be verified. It was not known when the video was filmed or when Ismail was taken hostage, but the shipment documents shown on the video were dated Jan. 5. His passport and Kuwaiti residency papers also were shown.

The United States hopes that an elected Iraqi government might command broader public support in the campaign against the insurgents, hastening the day when the 150,000 American troops could go home.

However, interim Prime Minister Ayad Allawi said it was too early to talk about a withdrawal of U.S.-led forces.

"The terrorists and the evil forces are trying to break our will. They are trying to stop democracy from happening in Iraq," Allawi said in an interview Sunday on British Broadcasting Corp. television.

Allawi said Iraqis ultimately want to see their own forces tackle the country's security problems.

"But it is too premature to talk about withdrawal," Allawi said.

"We wouldn't like to set a time at all. We would like to have the multinational forces helping us and training and developing both our army as well as our internal security forces."

Meanwhile, the Chinese Foreign Ministry confirmed Sunday that eight Chinese construction workers taken hostage by Iraqi insurgents have been safely transferred to Chinese custody. A day earlier their captors said they were releasing the men.