A Taliban homicide bomber blew himself up Thursday inside a mosque in southern Afghanistan, killing a deputy provincial governor and five other worshippers in the latest assassination of a senior official in President Hamid Karzai's government, officials said.

The attack came hours after a homicide car bomber struck an army bus in Kabul, killing a civilian and wounding four other people.

The twin-homicide attacks suggest the militants will continue their bombing campaign this year, after launching more than 140 homicide missions in 2007, the highest number since the ouster of the Taliban in the U.S.-led invasion of 2001.

The bomber in Helmand province struck inside a mosque in the provincial capital of Lashkar Gah, killing the deputy governor, Pir Mohammad, and the five others, provincial police chief Mohammad Hussein Andiwal said.

The blast also wounded 18 people, including two children, and damaged the mosque walls, Andiwal said.

Zabiullah Mujahid, a spokesman for the Taliban, said an Afghan from the eastern Paktia province, Qudratullah, carried out the attack. His claim could not be independently verified.

Mohammad had served as a deputy governor of Helmand for the past five years. He had two wives and 11 children, said Sher Mohammad Akhunzada, a former provincial governor.

Helmand is the center of world's opium and heroin production and scene of intense clashes between militants and British, American and Afghan government forces.

The Taliban often attack Afghan officials as part of their attempt to weaken the control of Karzai's U.S.-backed government. Provincial officials are the key component in attempts to extend government control and provide services in lawless areas of the country.

The militants have moved away from direct confrontations with superior foreign troops, which inflict heavy casualties on them. Instead, the militants increasingly resort to homicide and roadside bombings. Most of the victims of such attacks are civilians.

Last year, in Khost province homicide bombers tried three times to kill Gov. Arsallah Jamal. He survived all those attacks, but a number of his guards were killed.

In Sept. 10, 2006 a homicide bomber killed the governor of eastern Paktia province, Abdul Hakim Taniwal, outside his home. Another homicide bomber killed six people at his funeral the next day.

Andiwal said Mohammad had just arrived from a meeting at the nearby compound of the Helmand governor.

"After finishing his meeting, the deputy governor walked to the mosque for prayer," Andiwal said. "As they were praying, the bomber detonated his explosives."

The mosque's prayer leader was also killed, he said.

Haji Ikramullah, who was on his way to pray when the blast occurred, said he saw dead bodies inside and wounded people shrieking in pain.

The mosque blast happened hours after a homicide car bomber targeted an Afghan army bus in Kabul, killing one civilian and wounding four other people, officials said.

The blast shattered the bus windows and badly damaged a passing taxi in Kabul's Taimani neighborhood, said police officer Jan Agha. A soldier was among the wounded.

A series of attacks last year targeted buses carrying Afghan security forces, a key element of U.S. efforts to beat back the insurgency gripping the country's south and east. In two incidents alone 65 people, mostly soldiers, were killed.

More than 6,500 people -- mostly insurgents -- died in the violence last year, according to an Associated Press count of figures provided by local and international officials.

Meanwhile, in eastern Nuristan province militants beheaded four road construction workers and dumped their bodies on the side of the road Wednesday, said deputy provincial police chief Mohammad Daoud Nadim.

The four were kidnapped 10 days ago while working on a road project in Kamdesh district, Nadim said.

In Kabul, hundreds of people demanded the release of an Afghan journalist who was sentenced to death last week after he was found guilty of insulting Islam.

The demonstrators from the small, secular Solidarity Party rallied in front of the United Nations office in support of 23-year old Sayed Parwez Kaambakhsh, who was sentenced by a three-judge panel in the northern city of Mazar-i-Sharif for distributing a report he had printed off the Internet to journalism students.

The article asked why Islam permitted men to have four wives but women could not have multiple husbands.

Kaambakhsh has appealed his conviction.

International human rights groups have condemned the sentence but Afghanistan's upper house of parliament welcomed the ruling and criticized "international interference" in the matter.