A homicide bomber blew himself up inside a mosque in southern Afghanistan on Thursday, killing Helmand province's deputy governor and five other people, officials said.

The bomber struck in the provincial capital of Lashkar Gah, while people were praying inside the mosque, said provincial police chief Mohammad Hussein Andiwal.

Helmand's deputy governor, Pir Mohammad, was killed in the blast, said Nisar Ahmad, a provincial health official.

The blast killed five other people and wounded 11, Ahmad said.

Taliban regularly attack Afghan officials as part of their attempts to weaken the control of U.S.-backed President Hamid Karzai's government.

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

The mosque blast happened hours after another suicide bomber in a car 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 September a homicide bomber blew himself up in an army bus in Kabul, killing 28 soldiers and two civilians. In June a bomb ripped through a bus carrying police instructors in Kabul, killing 35 people.

Last year was Afghanistan's most deadly since the ouster of the Taliban in a U.S.-led invasion in 2001. More than 6,500 people — mostly insurgents — died in the violence, 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 to journalism students a report he had printed off the Internet.

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.