ISLAMABAD, Pakistan — Government officials in Pakistan placed the country on high alert yesterday after two powerful bomb blasts killed an estimated 31 people and injured 170 in two coordinated attacks in the city of Lahore.

The first blast occurred at about 9:30 a.m. inside the offices of the Pakistani Federal Investigation Agency as hundreds of staff members arrived for work, according to government officials. The devastating explosion partially sheared off one side of the building, blew out dozens of windows and left a deep crater in the ground.

The agency, officials said, is responsible for cases involving illegal immigration and smuggling. It is also the base for an American-trained counterterrorism unit.

The bombing in the heart of the capital of Punjab province appeared to come from explosives planted in a vehicle parked nearby, according to a spokesman for Pakistan’s Interior Ministry.

The Federal Investigation Agency’s director in Punjab, Chaudhry Manzoor, said he and at least 200 other officials were in the building when the bomb exploded. “I saw dozens of officials badly injured and some taking their last breaths,” he said. Mr. Manzoor said that several prisoners were also housed in the building but that none were injured.

The second blast was detonated around the same time as the first, when a suicide bomber drove a pickup truck into an advertising agency several miles away, in a residential area of Lahore called Model Town. A guard at the agency, Sabir Ahmad, said two men in the vehicle drove toward an outside gate at a high rate of speed before detonating their explosives. “The driver had a longish beard. I could not see the other guy sitting next to him properly,” Mr. Ahmad said. “But I saw two big cartons in the van. I asked them loudly why they were coming to the house. Then the driver just yelled at me to move away from the vehicle. A few seconds later, he smashed the truck into the building.”

The explosion, which occurred several hundred yards from the second residence of political leader Asif Ali Zardari, killed a man and two children who were playing nearby, government officials and witnesses said.

“The whole nation is deeply grieved and perturbed over these acts of sheer madness,” retired a spokesman for Pakistan’s Interior Ministry, Brig. Javed Iqbal Cheema, said at a news conference in Islamabad. “The law enforcement agencies are trying their level best to break the remnants of clandestine terrorist cells.”

Area hospitals were overrun with casualties and were placed on emergency status immediately after the blasts. Reports on the number of casualties varied. Mr. Cheema said 24 had been killed, but by late last night, local officials said there had been 31 fatalities. The bombings marked the second time in a week that Lahore, the cultural capital of Pakistan, has been targeted in violence, and the third attack in as many weeks against a high-profile government target.

Pakistan has been wracked by political unrest and violence since early last year, but attacks have intensified considerably since the assassination of former prime minister Benazir Bhutto on December 27. More than 100 people have been killed in violence since Pakistan held its national parliamentary elections on February 18.

Mr. Cheema said yesterday that the government has beefed up security in public areas and at government installations across the country. Provincial government officials have also been asked to review their plans and close any gaps in security.