Tuesday's shooting is the second such attack in just over two weeks, which happened on the outskirts of Quetta, the capital of oil and gas-rich Baluchistan, which borders Iran and Afghanistan.

According to Associated Press and the German Press Agency, four gunmen on motorcycles forced the bus to stop, lined up the passengers and shot them. Television footage showed the bus with bullet holes in the front windshield, engulfed in flames, with luggage scattered at the site. Police and paramilitary units quickly sealed off the area.

Ongoing attacks

Sunni extremists are suspected of carrying out the latest attack. On September 20, 2011 gunmen killed 26 Shiite pilgrims after ordering them off their bus in Mastung, a district 50 kilometres (30 miles) south of Quetta.

On September 4, 2010 a suicide bomber killed at least 57 people at a rally in Quetta.

International criticism

London-based human rights organisation Amnesty International says the killings highlight the failure of the Pakistani authorities to address sectarian violence across the country. Amnesty's Asia-Pacific director Sam Zarifi said that, "These are not random killings but demonstrate the deliberate targeting of the Shi'a (Shiites) by armed groups." These attacks proved that without an urgent and comprehensive government response, no place was safe for Shi'a Muslims. Amnesty says at least 15 attacks have been carried out which specifically targeted Shiites across Pakistan.

Pakistan's own independent rights watchdog said the killers had been emboldened by a persistent lack of action against sectarian militant groups, which have been implicated in thousands of deaths in past years. Pakistan's Human Rights Commission has warned that Tuesday's attack "exposes once again the diminishing writ of the state."

Pakistan is a majority Sunni Muslim state. Some 15 percent of the population are Shiite Muslims.

Agencies: Reuters, dpa, AFP (mj)
Editor: Grahame Lucas