Twin suicide car bombings have killed at least 30 people and injured many others in the Pakistani garrison city of Rawalpindi, officials have said.
One of the blasts hit a bus packed with members of the security forces.
Another explosion at a checkpoint left officers badly hurt, and there are fears the death toll will rise.
It came as former Pakistani PM Nawaz Sharif - ousted in 1999 by President Pervez Musharraf - said he would return to Pakistan from exile on Sunday.
Mr Sharif - leader of the Muslim League-N party - previously tried to return in September but was immediately deported back to Saudi Arabia.
Meanwhile Pakistan's Electoral Commission has confirmed Gen Musharraf's victory in last month's presidential election, ratifying a second five-year term.
The result was initially put on hold until a reconstituted Supreme Court verified Gen Musharraf's right to stand while remaining head of the armed forces.
Witnesses said the bus entered a compound housing Pakistan's Inter-Services Intelligence (ISI), followed by a small car, which blew up seconds later.
"We saw a burning bus and people from the army trying to put the fire out. I don't think anybody inside the bus could have survived," Shoaib Abbasi, who was working at a nearby hotel, was quoted by AFP news agency as saying.
Soldiers and police quickly sealed the scene, and forced bystanders and journalists back.
Both vehicles were destroyed in the blast, which also damaged surrounding buildings.
An intelligence agent at the scene told the Associated Press news agency that the destroyed bus was a 72-seater, but that more people were on board.
About 19km (12 miles) away, a bomber in a car also attacked the checkpoint, army spokesman Maj Gen Waheed Arshad said.
Reports from security sources said at least one officer died in the attack.
"Both were suicide attacks," Gen Arshad told local reporters.
Pakistan has recently seen a number of suicide bombings, including an attack in Karachi that killed at least 135 people.
This is the third recent strike on Rawalpindi, and the first since a state of emergency was imposed by Gen Musharraf.
Rawalpindi, near the capital, Islamabad, is the main headquarters of the army in Pakistan, and the place where Gen Musharraf has his military offices.
No group has yet claimed responsibility for the bombings.
But the BBC's Barbara Plett in Islamabad says attacks are often suspected to have been carried out by pro-Taleban militants in revenge for military operations in the tribal areas near the Afghan border and in North-West Frontier Province.
The country is in the midst of political turmoil. Gen Musharraf has imposed emergency rule, which critics say will undermine general elections scheduled for January.
Gen Musharraf has promised to step down as the army chief and serve his new term as a civilian.