Iran's (search) foreign minister made a historic trip to Baghdad on Tuesday, pledging to secure his country's borders to stop militants from entering Iraq and saying the "situation would have been much worse" if Tehran were actually supporting the insurgency as the U.S. has claimed.

Iranian envoy Kamal Kharrazi's (search) trip — two days after Secretary of State Condoleezza Rice paid a surprise visit to support the war-ravaged country's political process — was the highest-level visit by an official from any of Iraq's six neighboring countries since Saddam Hussein's ouster two years ago.

Kharrazi, who held talks with Iraqi Prime Minister Ibrahim al-Jaafari (search), President Jalal Talabani and Foreign Minister Hoshyar Zebari on a day of deepening sectarian violence, vowed that his country was committed to supporting Iraq's political and economic reconstruction and would do all it could to improve security conditions.

"We believe securing the borders between the two countries means security to the Islamic Republic of Iran," Kharrazi said.

Zebari said militants have infiltrated from Iran into Iraq "but we are not saying that they are approved by the Iranian government."

New British Defense Secretary John Reid also visited Iraq on Tuesday, traveling to Baghdad and Basra on his first foreign trip. The stream of visitors is aimed at shoring up the new Iraqi leadership caught in a surge of violence that has killed more than 470 people killed since the government was announced April 28.

Ties between neighboring Iraq and Iran improved after the ouster of Saddam, who led an eight-year war against Iran during the 1980s in which more than 1 million people died. Relations remained cool after that war, with Iran supporting anti-Saddam groups and the former Iraqi leader hosting the Mujahedeen Khalq, an Iranian militia that fought the Shiite religious regime in Tehran.

But since the U.S.-led invasion swept Saddam from power, Iraq's majority Shiite Muslim community has risen to power and worked to build close ties with Iran.

Iran, however, has been accused of supporting insurgents in Iraq to destabilize reconstruction efforts by the United States, which regards Tehran as a terror sponsor bent on producing nuclear weapons. Iran denies both claims.

Al-Jaafari, who led anti-Saddam militiamen based in Iran during part of his two-decade exile, has said Iraq now wants positive relations with Iran.

The Iranian envoy's visit comes at a time of spiraling violence fueled by foreign extremists and rival groups of Sunnis and Shiites.

U.S. troops backed by helicopters battled scores of insurgents holed up in two houses in Mosul, 225 miles northwest of Baghdad. Mosul police commander Lt. Gen. Ahmad Mohammed Khalaf claimed 20 militants were killed when U.S. aircraft destroyed the buildings, but the American military said it was unaware of any casualties.

Three Islamic clerics — a Shiite and two Sunnis — were shot and killed in Baghdad, police said Tuesday, a day after Iraq's prime minister vowed to use an "iron fist" to end sectarian violence.

Another 17 Iraqis were killed Tuesday: two Iraqi officials in separate Baghdad drive-by shootings, six truck drivers delivering supplies to U.S. forces north of the capital, a former member of Saddam's Baath Party and his three grown sons, three Mosul police officers and two soldiers in Baghdad.

An American soldier was killed and a second was wounded when a roadside bomb struck their patrol near Tikrit, 80 miles north of Baghdad, the military said. At least 1,622 U.S. military members have died since the Iraq war began in March 2003, according to an Associated Press count.

A militant group posted a video on the Internet Tuesday showing the slaying of two men said to be Iraqis who worked on American bases. Before they died one warned Arabs not to cooperate with the Americans.

The video, posted by the Ansar al-Sunnah Army on a Web forum known for its militant content, showed the two men confessing to working on bases in the western province of al-Anbar, one of them as a driver for the U.S. firm KBR, the other as a maintenance man.

"I advise every Iraqi, or Arab in general, against dealing with the American forces because it is unlawful," the driver, who identified himself as Tarek Ammouri, said to the camera.

The two men are then seen sitting, hands bound, outside in the dirt, and are gunned down with automatic weapons.

The video's authenticity could not be independently verified. The video and statement did not say when the men were abducted and when the killings took place.

The targeting of religious leaders is another disturbing development in Iraq's relentless insurgency.

Shiite cleric Sheik Mouwaffaq al-Husseini was killed in a Tuesday drive-by shooting by unknown gunmen in Baghdad's western Jihad neighborhood, police Capt. Taleb Thamer said.

A senior police officer, speaking on condition of anonymity, said Tuesday that two more Sunni clerics had been shot and their bodies found in Baghdad within a 24-hour period.

The two Sunni clerics, Sheik Hassan al-Naimi and Sheik Talal Nayef, were kidnapped Sunday from different mosques in Baghdad's northern Shaab neighborhood by men wearing Iraqi army uniforms, according to the police officer and Sheik Hamed al-Khazraji, a spokesman from the Sunni Muslim Association of Muslim Scholars.

"If these measures continue, they will lead the country, God forbid, into sedition that some foreign and internal groups seek," the association said in a statement that also demanded the defense and interior ministers resign.

Defense Minister Saadoun al-Duleimi has rejected government involvement in the killings, but said some killers have worn Iraqi army uniforms when kidnapping their victims. He also declared that Iraqi troops will no longer be allowed to enter mosques, churches or universities.

A statement purportedly released by Abu Musab al-Zarqawi's Al Qaeda in Iraq group criticized Rice's visit to Iraq on Sunday and her calls to include Sunni Arabs in the political process.

"The hag wants the participation of the apostates and secularists who are claiming to be Sunnis," the statement said about Rice. "You should know that our (the Sunni) way is fighting you."

Former Baath Party member Kanis Mohammed al-Janabi and his three sons, aged 17 to 25, were abducted and killed Tuesday in Tunis, a village within the notorious Triangle of Death about 20 miles south of Baghdad, police Capt. Muthana Khaled said.

The killers threw the bodies from a station wagon onto a road and sprayed the bodies with machine-gun fire before horrified onlookers, Khaled said.

Meanwhile, a spokesman for Australia's senior Muslim cleric said an Australian engineer being held hostage in Iraq could be released "very soon."

Sheik Taj El Din al-Hilaly, the Mufti of Australia, flew to Iraq last week to try to make contact with Douglas Wood's captors. He was also carrying medication to treat Wood's heart condition and an offer from his family to make a substantial donation to an Iraqi charity in return for his release.

A spokesman for al-Hilaly, Keysar Trad, said an anonymous man who claimed to represent Wood's captors phoned to say the kidnappers had received the medication and were preparing to release him.