Twenty beheaded bodies were discovered Thursday on the banks of the Tigris River southeast of Baghdad.

The beheaded remains were found in the Sunni Muslim village of Um al-Abeed, near the city of Salman Pak, which lies 14 miles southeast of Baghdad.

A parked car exploded next to commuters waiting at the stop in the capital's southern Al-Bayaa neighbourhood, killing 21 people and wounding 42, hospital and security officials said.

Iraqi security officials said the explosion occurred at around 8:15 am (0415 GMT) and expected the death toll to rise. A medic in the city's Yarmuk hospital confirmed receiving the bodies of 21 people killed in the blast.

The targeted neighbourhood, a mixed area in southwest Baghdad, often sees clashes between Shiite militiamen and Sunni insurgents, and has been hit by several car bombs during Iraq's sectarian conflict.

Although the area lies in the mostly Sunni western half of the city, US commanders there say the Shiite Mahdi Army militia maintains an intimidating presence and has driven many Sunnis from their homes.

The evictions have brought retaliatory car bombs and an escalating cycle of violence, despite the increased presence of US and Iraqi forces following the launch of a Baghdad security crackdown in February.

The increased presence has failed to prevent continued communal bloodletting including car bombings.

Four members of a family, including three women, were killed on Thursday when several mortar rounds struck their home in Baghdad's Al-Fadhel neighbourhood, witness Mohammed Saad said.

"Another man was wounded, with his legs blown off," he told AFP.

In the southern city of Basra, three British soldiers were killed and a fourth seriously wounded when a roadside bomb hit their foot patrol, military spokesman Major David Gell said.

"It is with deep regret that we can confirm that three soldiers were killed by an IED (improvised explosive device) this morning," Gell told AFP by telephone from Basra, adding that another soldier was seriously wounded.

Iraq's second city is a battleground between rival Shiite factions, and the 5,500-strong British force deployed there often comes under attack.

"The device detonated at approximately 1:00 am (2100 GMT) as they were conducting a dismounted patrol after getting out of their Warrior armoured vehicle in the Al-Antahiya district in southeast Basra," Gell said.

The deaths brought the total number of British casualties in Iraq to 156, and came a day after Britain's new Prime Minister Gordon Brown pledged to "learn the lessons that need to be learned" from his country's interventions in Iraq and Afghanistan.

The US military reported the death of one soldier in a similar roadside bomb in Baghdad, taking its losses to 76 in the month of June and 3,553 since the March 2003 invasion, according to an AFP count based on Pentagon figures.

The Paris-based media watchdog Reporters Without Borders said on Thursday that four more Iraqi journalists had been killed in the past three weeks.

One of the most recent victims was Rahim al-Maliki, a well-known poet who hosted cultural programmes on the state-run Iraqiya television network before he was killed in a Baghdad hotel bombing on Monday.

Another veteran reporter, Hamid Abd Sarhan, 57, was ambushed and killed as he drove home on Wednesday in the southern Baghdad district of Al-Saidiyah, the organisation said, citing the Journalists Union.

A third journalist, Aref Ali Falih, a correspondent for Aswat Al-Iraq (Voices of Iraq) was killed in a June 11 car bomb in the town of Khalis, northeast of the capital.

At least 187 journalists and media assistants have been killed since the start of the March 2003 US-led invasion. Two are missing and there has been no news of 14 others since they were kidnapped, according to the media watchdog.

Insurgents have also continued to target the country's dwindling religious minorities. On Wednesday night two members of a Christian cultural society in Mosul were found dead in the city centre, according to local police.

Police later identified one of the men, Luay Suleiman, as a reporter for Nineveh al-Hurra, a local newspaper.