A roadside bomb destroyed a second heavily armored Bradley Fighting Vehicle (search) in less than a week Monday, killing two U.S. soldiers, wounding four others and indicating that insurgents have increased the power of the explosives they are using against American troops.

The blast came hours after gunmen in a passing car assassinated Baghdad's deputy police chief and his son while they drove to work, part of a campaign to target Iraq's security forces. Al Qaeda in Iraq, the group led by Jordanian terrorist Abu Musab al-Zarqawi (search), claimed responsibility.

American officials have cautioned that insurgents will escalate attacks in a bid to scuttle Jan. 30 elections. After a roadside bomb struck a Bradley on Thursday and killed seven soldiers, the Defense Department warned that militants were increasing the size and power of their bombs.

The attack Monday on a Bradley in southwest Baghdad (search) followed the same pattern.

"It's fair to say that they are afraid of the elections, they are afraid of what the outcome will be and they want to do everything they can to derail that process because that's just one more step toward their demise," U.S. military spokesman Lt. Col. James Hutton said. "This is probably an indication of their increase in effort and investment to derail the vote."

The attack was one of several acts of major violence Monday.

An attacker detonated a bomb in a fake police car at a police station courtyard in Baghdad, killing at least four officers and wounding 10 during a shift change, police and witnesses said.

A roadside bombing killed three Iraqi National Guard soldiers and wounded six during a joint patrol with U.S. troops in the restive northern city of Mosul, said Maj. Andre Hance, a U.S. military spokesman. He said there were no American casualties.

In a suggestion that the insurgents were looking for new ways to intimidate voters, a militant group posted threats in at least two towns warning it would deploy "highly trained" snipers to target voters around Iraq during the elections.

The statement, signed by the previously unknown Secret Republican Army, said 32 snipers will stalk voters outside polling in Wasit, a largely Shiite province south of Baghdad that includes Kut, Numaniyah and Suwaiyra. It did not say how many would be sent elsewhere.

Sheik Fassal Raikan al-Gout, the governor of Anbar province, said he was aware of the circulated posters but dismissed their importance.

"We do not care about such statements," he said. "We will continue to do our best and what we see fit to maintain security."

Sunni Arabs, who make up about 20 percent of Iraq's estimated 26 million people, say the country is far too dangerous for the vote later this month, and many are refusing to participate. Failure by the Sunni Arabs to participate in the vote would undermine the election's credibility.

But the United States rejected a request by Sunni Muslim clerics to spell out a timetable for withdrawing troops from Iraq in exchange for calling off their boycott of the elections, U.S. Embassy spokesman Bob Callahan said.

The leader of Iraq's largest Shiite Muslim political group said in an interview broadcast Monday that "if elections were postponed, this will lead to a serious legal problem because Iraq will be without a legitimate authority."

"No legitimate authority has the right to postpone the elections because this will lead to more problems," said Abdul Aziz al-Hakim, head of Supreme Council for the Islamic Revolution in Iraq. He was referring to the interim constitution and a U.N. resolution that says elections must be held before the end of January.

A number of election officials and government leaders have already fallen victim to brutal terror attacks, and many have received death threats. The most prominent victim in recent weeks was the governor of Baghdad, Ali al-Haidari, who was slain with six bodyguards on Jan. 4.

On Monday, attackers shot and killed Baghdad's deputy police chief, Brig. Amer Ali Nayef, and his son, Lt. Khalid Amer, also a police officer. They were slain in Baghdad's Dora district while traveling in a car on their way to work, Interior Ministry spokesman Capt. Ahmed Ismail said.

Gunmen sprayed machine-gun fire from two cars driving parallel with the police chief's vehicle close to his home before fleeing, police said. The two were alone in the car.

The government sought to strike back against the insurgents with its own media campaign Monday. Interim Prime Minister Ayad Allawi said authorities have captured 147 suspected insurgents in Iraq, including the new leader of an insurgent group.

Allawi identified the man as Raad al-Doury, who just days earlier had taken over the top post of Jaish Muhammad -- Arabic for Muhammad's Army -- from a man detained in November. Allawi has accused Jaish Muhammad of killing and beheading a number of Iraqis, Arabs and foreigners in Iraq.

"Every day the terrorists name a new leader we capture him and they will stand trial," Allawi said.

Soon after, the Al-Arabiya television station showed footage of four Iraqis confessing that they had carried out killings and beheadings of Iraqi intellectuals as well as members of Iraq's security. The four said they were forced to do the job or otherwise get killed.

Also Monday, the U.S. military said its forces accidentally killed a 13-year-old Iraqi girl and wounded a 14-year-old boy near Baqouba, 35 miles northeast of Baghdad.

"This is an absolute tragedy. We do not know at this time what the children were doing in the area," said a military spokesman, Maj. Neal O'Brien. "An investigation into what happened is under way."