BAGHDAD, Iraq — A distraught American hostage appeared on television with automatic weapons trained on his head yesterday, a day that recalled the darker periods of Iraq's insurgency as bombs killed at least 14 people and U.S. Marines clashed with insurgents near the Syrian border.

In a videotape broadcast on al-Jazeera television, Jeffrey J. Ake, 47, of LaPorte, Ind., apparently reading from a statement, asked the United States to start a dialogue with Iraqi insurgents, to start withdrawing its forces from Iraq and to save his life.

The White House announced that authorities were monitoring the situation but would not negotiate for Ake's release. Ake was kidnapped Monday from a water-treatment facility near Baghdad, where he worked as a contractor on a reconstruction project.

Meanwhile, four other American contractors were among those wounded yesterday by a car bomb that killed five Iraqis in Baghdad. The victims were traveling between the capital and the nearby airport in a Defense Department convoy when the bomb detonated.

Al-Qaida in Iraq, the insurgent group led by a Jordanian guerrilla, Abu Musab al-Zarqawi, asserted responsibility for the attack in an Internet statement.

In northern Iraq, a bomb killed at least nine Iraqi police officers as they were defusing another explosive device planted beneath an oil pipeline near Kirkuk. They had successfully disabled one bomb — apparently a decoy — only to have a second, hidden bomb explode nearby. Five Iraqis were wounded in the incident.

And on Iraq's long border with Syria, U.S. Marines battled guerrillas claiming ties to al-Qaida for a third straight day. The U.S. military said yesterday that Marines had killed 30 insurgents Monday and Tuesday as they repeatedly attempted to overrun an isolated Marine outpost and a nearby Iraqi army outpost.

Insurgents said fighters from al-Zarqawi's organization and the Iraqi insurgent group known as Mohammad's Army were fighting together against U.S. forces in the nearby city of Qaim.

A statement posted in mosques in Qaim, purportedly by al-Qaida in Iraq, threatened attacks on U.S. bases and other targets around Iraq if American forces did not withdraw from the city in 12 hours.

Ake is president and CEO of Equipment Express, whose products include machines that fill water bottles, The Associated Press reported.

More than 200 foreigners have been kidnapped in Iraq in the past year. Dozens have been killed, including several Americans.