BAGHDAD, Iraq - Marines backed by fighter jets fought a fierce battle with insurgents in Fallujah today, killing 13 Iraqis and wounding 14 others, as Secretary of State Colin Powell made an unannounced visit to Baghdad.

"We are facing challenges in the weeks ahead that we are determined to overcome," Powell said after meeting with Interim President Ghazi al-Yawer.

Powell's visit followed a decision Thursday by Iraqi authorities to abruptly postpone a national conference of political, religious and civic leaders considered a crucial step on the road to democracy.

Officials said the two-week delay of the gathering - which by law was to have been held by the end of July - came at the request of the United Nations, which hoped to persuade more Iraqis to participate even as key factions threatened to boycott and others failed to choose a delegate. Officials insisted pushing the event back would have no effect on the country's first democratic elections, scheduled for January.

"We didn't want to postpone. It was upon the strong recommendation of the United Nations that we postponed for two weeks," al-Yawer said today.

A militant group set a deadline for today to behead one of seven foreign truck drivers if its demands, including a pullout by their company, were not met. The Kuwaiti company said it was sending an official to Iraq to work with Sheik Hisham al-Duleimi, head of an organization of Iraqi tribal leaders trying to negotiate the hostages' release.

Al-Duleimi told The Associated Press that he has been negotiating with Egyptian and Indian officials regarding the captives, but had not yet spoken to the kidnappers.

"I appeal to the kidnappers to be patient and to refrain from beheading one of the hostages and to extend the deadline until positive results can be reached," he said.

In northern India, villagers detained 37 foreign tourists, most of them from Britain, to protest the kidnapping of the three Indian workers in Iraq, police said today.

The tourists, traveling in two buses, were stopped Thursday night near Santoshgarh village in Una district, the home region of two of the three Indian truck drivers being held hostage by unknown kidnappers in Iraq.

Overnight in Fallujah, U.S. Marines and Iraqi troops engaged for hours in a battle with insurgents, the military said. Witnesses reported hearing scores of mortar rounds fired toward the city's eastern edge, where Americans are based, and planes flying overhead.

The military said the fighting began when insurgents attacked a joint patrol of Marines and Iraqi troops with gunfire, mortars and rocket propelled grenades. The troops responded with gunfire, tank fire and aircraft bombing raids, which hit a building the insurgents had fled to, the military reported.

Twelve auto repair shops and two houses were destroyed as a result of the clashes. U.S. Marines said they suffered no casualties.

Dr. Salim Ibrahim at Fallujah General Hospital said 13 Iraqis were killed and 14 others wounded in Fallujah, a turbulent city west of Baghdad. Many of the bodies had been torn apart in the bombings, and Ibrahim said the death toll could change as officials identified remains.

Al-Yawer said the recent surge in the attacks, including a car bombing outside a Baqouba police station Wednesday that killed at least 70 people, showed insurgents were growing more desperate.

"I think the bad guys, the enemy, the army of the darkness is getting more helpless and hopeless. That is why they are stepping up these things. Time and the place is on our side," al-Yawer said.