ISLAMABAD, Pakistan  A suicide attack Thursday on a bus in Rawalpindi was the first that singled out workers of Pakistan’s prized nuclear labs, military analysts and prominent national newspapers said, raising new questions about the government’s ability to withstand increasingly bold assaults by the Taliban against the country’s military complex.

The attack comes as Pakistan’s army is fighting the Taliban on several fronts and is about to begin an even more ambitious campaign in the insurgents’ heartland in Waziristan.

Government officials have said that the attack hit a bus carrying workers from a nonnuclear military plant, but military analysts said they believed that was an effort to avoid the embarrassment of admitting that a vehicle connected with the nuclear program had been hit.

The Taliban and Al Qaeda have announced that their goal is to topple the government and gain control of its nuclear arsenal. Singling out nuclear workers, even though they were miles outside the weapons lab, military analysts say, carries heavy symbolism in a nation that believes its ultimate strength lies in its nuclear capability. It also suggested a worrisome level of sophistication.