At least 24 people have been killed in two bomb blasts near the Pakistani military headquarters in the city of Rawalpindi, the military says.
The bus was completely destroyed in the blast
The first explosion took place on a bus carrying defence employees in the town near Islamabad, killing 17 people.
Shortly afterwards, a motorcycle bomb exploded in a market, killing seven people.
Attacks by militants have increased since the army stormed the Red Mosque in Islamabad in July.
It had been occupied by pro-Taleban extremists and at least 100 people were killed during the siege and subsequent military operation.
Since then, suicide attacks and bombings, particularly in the tribal areas, have claimed the lives of at least 60 Pakistani soldiers.
The BBC's Damian Grammaticas, in Islamabad, says these latest attacks will cause particular concern because they have happened in what is a military zone.
They come at a time of great political uncertainty in the country with former prime ministers Nawaz Sharif and Benazir Bhutto promising to return to the country to challenge the rule of President Pervez Musharraf.
At least 66 people have been injured in the two attacks, officials said.
The first explosion occurred at 0720 (0220 GMT).
At least 17 defence employees were killed when a bomb tore through their bus near Qasim market in Rawalpindi.
Eyewitnesses said the bus was completely destroyed by the blast which could be heard across the city.
The roof of the bus and all its windows were blown away.
"There was a huge bang, then I saw the bus in a mangled heap. Body parts were scattered across the road and there was blood everywhere," witness Mohammad Tahir told AFP.
One of the dead in the bus attack has been confirmed as a sergeant in the intelligence services, according to the list issued by the hospital. A relative told the BBC the rest of the men on the bus were his colleagues.
Television pictures showed rescue workers at the scene, trying to cut open the wreckage to pull out injured people and bodies.
The second blast happened about three kilometres (two miles) away when a suspected motorcycle bomb exploded in the city's RA Bazaar.
"We only know that it was a motorcycle bomb. It exploded with a big bang," a police official was quoted as saying by the Associated Press.
Military spokesman Maj-Gen Waheed Arshad said authorities were trying to determine which department the people on board the bus worked for.
"It's terrorism because innocent people were killed in both blasts," Maj-Gen Arshad said.