BAGHDAD — A car bomb exploded yesterday at an outdoor market in a Shiite area of Baghdad, killing 25 people and wounding at least 60 — the deadliest in a string of attacks that stoked sectarian tension in and around the capital.The blast occurred in Amil, one of a cluster of neighbourhoods in southwestern Baghdad where Sunni-Shiite tension is running high three months after the start of the US-led security crackdown.

Following the blast, terrified survivors ran through the streets hauling buckets and pots of water to try to put out fires in shops that were shattered by the bomb. Volunteers tore through the rubble, searching for survivors.

Sami Hussein, 25, was heading to the market with her five-year-old son when she heard the explosion, “followed by gray and black smoke, which engulfed the market and made me to fall on the ground.”

She suffered shrapnel wounds in her face and legs.

“I lost my son, and have no idea about his fate,” she said. Medical officials at the hospital said he died in the blast.

Fadhil Hussein, 32, who sells spices in the market, said he was thrown from his stall and wounded with shrapnel in his back and head.

“I found myself in a pickup truck with other people. Some of them were bleeding and yelling,” he said.

No group claimed responsibility for the blast. But US officials believe Sunni extremists are stepping up car bombings, especially against Shiite civilians, to enflame sectarian hatred and undermine public confidence in government security forces.

There were other signs yesterday that Sunni-Shiite tensions are again rising after they eased last winter following the start of the Baghdad security operation February 14.

In north Baghdad, gunmen wearing army uniforms stopped a bus carrying college students to a Shiite neighbourhood, entered the vehicle and sprayed the passengers with gunfire, police said. Eight students were killed and two were wounded.

At another fake checkpoint near Baqouba, 35 miles northeast of Baghdad, gunmen killed six people from one family — a woman, her five-year-old son and four men — and stole their car, police said. It was unclear whether the victims were Sunnis or Shiites.

In Baghdad, mortar shells struck a college in the mostly Sunni neighbourhood of Azamiyah, killing four people and wounding 27. Four rounds landed around the office of prominent Sunni politician Adnan al-Dulaimi, causing no casualties but destroying three cars, his staff said.

Gunmen in two vehicles ambushed a car in the mostly Sunni neighbourhood of Khadra carrying three plainclothes police officers from the major crimes unit, killing two and wounding the third, police said.

Another officer was killed when a roadside bomb exploded next to a police patrol driving through an eastern Baghdad neighbourhood, police said. Three other officers were wounded.

In all, at least 100 Iraqis were killed or found dead nationwide yesterday, according to police. They included 33 people found shot execution-style — presumably by sectarian death squads — and their bodies scattered across Baghdad.

South of the capital, US and Iraqi troops endured temperatures of 115 degrees as they trudged through canals waist-deep in sewage, searching for three American soldiers abducted in a May 12 ambush. Four Americans and one Iraqi soldier were killed in the attack.

At least three Iraqis were detained for questioning yesterday, but there was no sign of the missing 10th Mountain Division soldiers. An al-Qaida front group claimed it captured the soldiers but has posted no pictures of them on the Internet or offered other evidence to support the claim.

With violence raging, Prime Minister Nouri al-Maliki warned Iraqis that they face a long and difficult struggle to combat terrorism — even as pressure mounts in the United States to bring the US role here to an end.

“Our battle against terrorism is open-ended and long and no one should think that this battle will end today or tomorrow,” al-Maliki said in a televised speech marking his first year in office.

“The security challenges facing Iraq are very grave and what is making them worse is foreign meddling and the response and submission of some political powers to the influence of several nations,” which he did not name.

US officials have accused Iran of arming and training Shiite militias. They have also accused Syria of failing to stop Sunni extremists from transiting its territory to join the fight in Iraq.

Al-Maliki, a Shiite, also said the government will promote local “salvation councils” to rally public support against extremists. The councils will be modelled after an alliance of Sunni Arab clans that banded together in the western Anbar province to drive out al-Qaida.

“I call on the faithful and patriotic clans to set up national salvation councils in all of Iraq’s provinces and stand by the armed forces in the fight against terrorism,” al-Maliki said.

During a briefing yesterday for reporters, the US deputy commander in Anbar said that al-Qaida “has been expelled out of the population centres” in the province and that the arrival of additional American troops “will permit us to continue the pursuit of al-Qaida.”

“But there are still very real security issues that need to be dealt with,” Brig. Gen. John Allen said. “But I am optimistic that there have been significant progress and we will continue progress.”

Some US officers have been sceptical that the Anbar formula can work in other parts of the country, which have religiously and ethnically mixed populations. Anbar is heavily Sunni, and tribal loyalties are strong.