Two suicide attackers hit a military checkpoint in southwestern Pakistan on Thursday, killing 10 people, officials said. The army said the assailants detonated their explosives near a line of vehicles waiting at the checkpoint in Quetta, the capital of Baluchistan province. Deputy police chief Rehmatullah Niazi said three soldiers died in the first explosion. Seconds later, a second blast killed two more soldiers, one policeman and four civilians, Niazi said. He said 10 people were wounded, four of them seriously. Reporters at the scene said security forces sealed off the area, which is close to a sector of the city housing sprawling military installations. Two helicopters circled overhead, training powerful spotlights on the area where the after-dark attack occurred, while military ambulances carried away the injured. The attack adds extra charge to Pakistan's already fraught election campaign. Opposition leader Benazir Bhutto was due in Quetta on Saturday to stump for votes in the Jan. 8 parliamentary vote. A turbulent city close to the Afghan border, Quetta has seen regular bombing and shooting attacks. Many are linked to sectarianism and a low-key insurgency by Baluch nationalists seeking greater autonomy for their resource-rich but impoverished province. However, suicide attacks are more typical of Islamic extremist groups aligned with the Taliban and al-Qaida who are battling the army in several regions along the wild frontier. On Monday, a suicide car bomber wounded five children on an air force bus carrying them to school near Kamra, about 50 kilometers (30 miles) northwest of the capital, Islamabad. A similar attack killed 12 people the day before in Swat, a northern valley where the army is battling followers of a pro-Taliban cleric. Western officials have claimed that Taliban leaders are living unmolested in the Quetta area, which lies across the border from militancy plagued southern Afghanistan - an allegation hotly denied by the Pakistani government.