ISLAMABAD, Pakistan — President Gen. Pervez Musharraf faces a potent challenge Sunday with the return from exile of the religiously conservative elected leader he overthrew eight years ago.

Former Prime Minister Nawaz Sharif is expected to arrive in the eastern city of Lahore with the country still reeling from a set of brazen suicide attacks. Many Pakistanis are angry that a recently declared state of emergency has muzzled Musharraf's critics but not quelled militant violence.

Suicide bombers killed up to 35 people in the nearly simultaneous blasts early Saturday at the heart of Pakistan's security establishment.

In the first attack, an explosive-laden car rammed a bus carrying employees of Inter-Services Intelligence, Pakistan's spy agency. Moments later, a bomber hit an army checkpoint in another part of the garrison city of Rawalpindi, 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 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.

The explosions were a bloody reminder that the nation's challenges go beyond the merely political and that the emergency Musharraf declared on Nov. 3 has done little to dampen the resolve of extremists.

Musharraf's opponents note that most of those he has targeted have been political opponents, lawyers and members of the media, rather than the militants leading an increasingly formidable insurgency.

Sharif, who has been living in exile in Saudi Arabia since shortly after his 1999 ouster, was expected to arrive in Lahore on Sunday afternoon, along with his brother and other family members, said Sadique al-Farooq, a senior leader of Sharif's Pakistan Muslim League-N party.

Al-Farooq said that thousands were expected to turn out to greet the returning politician, a staunch critic of Musharraf who is seen as having broad political support.

Sharif's return could prove challenging for Musharraf, particularly if he makes an alliance with Bhutto. But it is also a potential boon for the general, allowing him to claim that January's parliamentary elections mark a genuine return to democracy.

After Musharraf overthrew Sharif, he gave the jailed politician a choice: accept 10 years of exile or face life in prison on charges including hijacking and terrorism. The charges stemmed from Sharif's desperate attempts to turn away a packed civilian plane carrying Musharraf — then the army chief — back from a trip abroad.

As the Pakistan Airways plane ran low on fuel, Musharraf used the cockpit radio to contact his senior commanders on the ground, who quickly took over the country. By the time the plane touched down in the southern city of Karachi, Musharraf was Pakistan's new leader and Sharif was under arrest.

Sharif has been angling for a return ever since. In September he boarded a flight from London to Islamabad, but police in the Pakistani capital swiftly bundled him back onto a flight to Saudi Arabia.

This time, the outcome is likely to be different, with the Saudi leadership reportedly pressuring Pakistan to accept him. A close aide to Musharraf said Sharif would not be deported again.

"This time he will not be sent back," said Sheikh Rashid Ahmed, a former Cabinet member who remains a close adviser to the general.

Major opposition parties — including Bhutto's Pakistan People's Party — have been lining up to take part in the Jan. 8 vote, taking preliminary steps such as filing nomination papers. Bhutto said Friday she had not yet decided whether to take part, but that she was leaning toward participating.

On Saturday, a loose coalition of opposition groups including Sharif's PML-N announced it would boycott the voting unless the government lifts the state of emergency, restores sacked Supreme Court justices and releases all political prisoners within four days.

Also Saturday, Pakistan's electoral commission formally ratified Musharraf's election for a second five-year term as president. The move, widely expected after Musharraf's hand-picked justices on the Supreme Court approved his election Friday, paves the way for the president to resign from the army and rule as a civilian.

He has pledged to leave his army position and take the oath of office as president by the end of the month.