Baghdad, Iraq ? Insurgents gunned down four U.S. Marines on Monday west of Baghdad, while South Korea awaited word on the fate of a kidnapped worker after the deadline for his execution passed.

A U.S. Army soldier was killed Monday 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.

A videotape delivered to Associated Press Television News showed four Marines 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.

Brig. Gen. Mark Kimmitt, coalition deputy operations chief, confirmed the killings but gave few details. He said a U.S. quick-reaction force found the bodies after the troops failed to report to their headquarters as required.

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.

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.

Today, a South Korean Foreign Ministry official said the government could not say whether Kim Sun-il was still alive.

Kim, 33, who works for a trading company in Baghdad, was believed to have been kidnapped about 10 days ago.

“We have various intelligence and information on that matter, but we cannot give you a definite answer,” said ministry spokesman Shin Bong-kil.

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.

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

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.

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.