A U.S. quick reaction force has found the bodies of four U.S. Marines gunned down west of Baghdad on Monday, said Brig. Gen. Mark Kimmitt (search), coalition deputy operations chief.

Troops searched for the missing service members after they failed to report to their headquarters as required, Kimmitt said.

The Marines were conducting security and stability operations in Ramadi (search), a U.S. military spokesman in Baghdad told Fox News.

A videotape delivered to Associated Press Television News showed four Americans in uniform lying dead in what appeared to be a walled compound in Ramadi, an insurgent stronghold 60 miles west of Baghdad. One of the Americans was slumped in the corner of a wall.

The bodies had no flak vests — mandatory for U.S. troops in contested areas — and at least one was missing a boot. One fieldpack was left open next to a body as if the attackers had looted the dead before fleeing.

American officials had been concerned about the deteriorating security situation in Ramadi, located along a belt of Sunni militancy running westward from Baghdad along the Euphrates River.

Last week, seven Iraqi Civil Defense Corps (search) members were arrested for planting a roadside bomb that killed a policeman and wounded seven civilians in Ramadi.

Also Monday, a U.S. Army soldier was killed and seven others were wounded in a mortar attack in north-central Baghdad, the U.S. command said. The casualties indicated no let-up in attacks against Americans as the June 30 transfer of sovereignty draws near.

Meanwhile, South Korea said it would go ahead with plans to send thousands more troops to Iraq despite a threat by Iraqi kidnappers to kill a South Korean seen pleading for his life on a videotape.

Most of the kidnappings of foreigners over the past two months are believed to have occurred along that belt.

The South Korean government said it would go ahead with plans to send 3,000 troops to Iraq despite a threat by an Islamic extremist group to kill a South Korean man seen begging for his life on a videotape broadcast Sunday night by the Arab satellite television station Al-Jazeera.

"Korean soldiers, please get out of here," the man, Kim Sun-il, screamed in English. "I don't want to die. I don't want to die. I know that your life is important, but my life is important."

Kim, 33, who works for a trading company in Baghdad, was believed to have been kidnapped about 10 days ago. The kidnappers claimed to be from the Monotheism and Jihad group led by Jordanian-born terrorist Abu Musab al-Zarqawi (search), who is believed to have ties to Al Qaeda.

The kidnappers set a deadline of 24 hours from sunset Sunday for the South Koreans to comply or they would "send you the head of this Korean, and we will follow it with the heads of your other soldiers."

However, hours after the deadline passed, there was no word on Kim's fate and Al-Jazeera said it had received no new message from the kidnappers.

Once the deployment is complete, South Korea will be the largest coalition partner after the United States and Britain. South Korea now has 600 military medics and engineers in the southern city of Nasiriyah.

South Korean medics in Nasiriyah suspended free medical treatment to Iraqi patients because of security concerns stemming from the kidnapping, said Maj. Chun Heung-soo, a Defense Ministry spokesman in Seoul. He said the action should not be interpreted as a protest.

Hundreds of protesters attended a candlelight vigil in Seoul Monday to demand the government reverse its decision to send more soldiers to Iraq.

On Saturday, a U.S. airstrike destroyed a house in Fallujah, 30 miles west of Baghdad, that the United States said was a hideout for the al-Zarqawi group. Kimmitt told reporters the attack killed "key personnel in the Zarqawi network" but he would not confirm that any foreign fighters were among the dead.

Iraqi officials in Fallujah, long one of the centers of anti-American militancy, maintain the attack killed only Iraqi civilians. The Iraqi Health Ministry said at least 17 people died.

Chanting anti-U.S. slogans, hundreds rallied in Fallujah on Monday to protest the American airstrike. Demonstrators accused the Americans of falsely claiming that al-Zarqawi had sought refuge in Fallujah to create an excuse to attack the city.

Elsewhere, five Iraqi contractors were killed Monday in an ambush on their three-vehicle convoy 30 miles south of Mosul. The U.S. command said two others were wounded.

The recent kidnappings and attacks appear aimed at undermining the interim Iraqi government set to take power June 30, when the U.S.-led occupation formally ends. U.S. and Iraqi officials have vowed to go ahead with the transfer.

Coalition spokesman Dan Senor said that by week's end, all Iraqi government ministries would be under full Iraqi control.

Interim Prime Minister Iyad Allawi has promised to crush the terrorist threat and said Sunday his administration was considering martial law in some areas to restore law and order.

"They are trying to destroy our country, and we are not going to allow this," Allawi said.

But the interim president sought to temper those remarks Monday, saying martial law was only one of several steps under consideration.

President Ghazi al-Yawer said during a meeting with a U.S. congressional delegation that Allawi's remarks were in response to a "hypothetical question asked to a member of the government."

"It's our right," al-Yawer said, while adding it was not certain to be employed. "But it's an option that we are not ruling out. If we need to do so in order to preserve our security we will do so in a way that will not pose problems to the Iraqi public."

Also Monday, Iraq resumed oil exports six days after attackers blasted pipelines carrying crude oil to the Basra terminal on the Persian Gulf. Iraqi officials have announced stepped-up measures to protect the oil industry — the foundation of the nation's economy.

Resumption of oil exports followed intense efforts to repair the damaged pipeline. The country's other major export line, which runs from the northern oilfields to the Turkish port of Ceyhan, has been out of service since May 27 because of sabotage.

Analysts and traders said halting exports costs Iraq about $65 million in lost oil revenue daily.

Iran said Monday it had impounded three British military vessels and detained eight armed crewmen in the Shatt-al-Arab waterway, Iraq's main link with the Persian Gulf, for entering Iranian territorial waters.

Britain confirmed it had lost contact with a patrol of a three small vessels that Royal Navy personnel were delivering to an Iraqi river patrol. It said Britain was in contact with Iran to determine the circumstances of the seizure.

The waterway that divides Iran and Iraq has long been a source of tension. The 1980-88 Iran-Iraq war broke out after then-Iraqi leader Saddam Hussein claimed the entire waterway.

Monday's incident follows a strain in Iranian-British relations after London last week helped draft a resolution rebuking Iran for past nuclear cover-ups.

The Associated Press contributed to this report.