Militants struck at the heart of Pakistan's security establishment Saturday, killing up to 35 people in homicide attacks on a checkpoint outside army headquarters and a bus carrying intelligence agency employees, officials said.

The brazen early morning attacks coincided with the announcement that Nawaz Sharif, a former prime minister overthrown in 1999 by the country's current military leader Gen. Pervez Musharraf, would return from exile Sunday.

Sharif, one of Musharraf's most strident political foes, may contest parliamentary elections scheduled for January.

"Nawaz Sharif and other members of his family are coming back to (the eastern Pakistani city of) Lahore on Sunday," said Sadique al-Farooq, a senior leader of Sharif's Pakistan Muslim League-N party.

The homicide attacks came as Pakistan remained under a state of emergency, which Musharraf declared on Nov. 3, justifying it by citing the escalating danger posed by Islamic extremists. His critics have noted, however, that many of his moves have been against political opponents — including members of the judiciary, journalists and other moderates.

The two suicide attackers struck in Rawalpindi, a garrison city just south of the capital, Islamabad, just before 8 a.m., as employees were arriving for work.

In the first attack, an explosive-laden car rammed a bus carrying employees from the Inter-Services Intelligence agency, or ISI. The other bomber hit an army checkpoint in another part of the city, said Mohammed Afzal, a local police official.

Two senior intelligence officials — one of them at the scene — said at least 35 people were killed. They asked for anonymity, citing the sensitivity of their work.

An army statement said it could only confirm that 15 were killed in the attack on the bus, as well as the suicide bomber. It said that two security forces personnel were critically injured in the second attack, and that the bomber died.

"We suspect that pro-Taliban militants who are fighting security forces in our tribal areas are behind this attack," the intelligence official said, adding the injured and dead were being transported to hospitals.

The intelligence agent at the scene said that the destroyed bus was a 72-seater, but that it was badly overloaded and more people were believed on board. The army statement said 50 were on the vehicle.

After the blast, troops and police quickly cordoned off the area. They pushed back bystanders and snatched cameras and mobile phones from journalists and bystanders. Agents fanned out across the area, picking up pieces of metal that appeared to be from the bomber's car.

Shoaib Abbasi, owner of the Oriel guesthouse across from the intelligence compound, said that when he came out on the street after the blast, the bus was burning fiercely.

"Firemen tried to open the emergency doors while they were dousing the interior, but I can't believe anyone inside survived because of the intensity of the fire," he said.

Khyzer Hayat, the owner of a nearby grocery store, said the blast occurred at 7:40 a.m. "After the explosion, I went out on the street and found the ignition switch for a car amid the debris (which) I later gave to an intelligence agent," he said.

Musharraf condemned the blasts and sent his condolences to victims' families. He said the attacks would not deter his government's resolve in fighting terrorism, according to Pakistan's state news agency.

Tension between militant groups and Pakistan's military are high due to an ongoing military operation to sweep pro-Taliban fighters from the northern Swat valley, where authorities say more than 300 militants have been killed in recent weeks.

Saturday's attack was the second major strike against the intelligence agency in recent months. On Sept. 4, a suicide attacker blew himself up after boarding a bus carrying ISI employees, while a roadside bomb went off near a commercial area in Rawalpindi within minutes. At least 25 people were killed.

Islamic militants have launched dozens of suicide attacks this year. Most have taken place near the Afghan border, but several have taken place in the country's main cities, raising fears that violent extremism is spreading.

A bomber blew himself up in Rawalpindi on Oct. 30 at a checkpoint several hundred meters (yards) from Musharraf's office, killing seven people. Two weeks earlier, a suicide attack on opposition leader Benazir Bhutto's homecoming parade killed more than 140 people in Pakistan's largest city, Karachi.

Both Bhutto and Sharif have been barred from returning to Pakistan for the past eight years. But with Musharraf — who has just been re-elected as president for another 5-year term by a legislature packed with his allies — under international pressure to restore civilian rule, they now appear likely to allow their respective parties to contest the upcoming parliamentary vote.

The last time Sharif attempted to return to Pakistan, police swiftly bundled him back onto a flight to Saudi Arabia, where he has been living since shortly after Musharraf overthrew him in 1999.

But a close aide to Musharraf said Sharif would not be deported again. "This time he (Sharif) will not be sent back (to exile)," said Sheikh Rashid Ahmed, a former Cabinet member who remains a close adviser to the general.

If allowed to enter the country, Sharif would arrive in time to meet a Monday deadline for filing nominating papers for the Jan. 8 vote.

A senior official at the presidency said Friday that Musharraf had "softened" his stance toward Sharif, and was hoping for some level of reconciliation — raising the possibility that Musharraf might try to ally himself with the man he toppled, in order to freeze Bhutto out.

The official, who spoke on condition of anonymity because of the sensitive nature of the issue, said close associates of Sharif and Musharraf were in contact to see how they could end their feud.