A bomb blast has killed at least 19 people on the outskirts of Pakistan's northwestern city of Peshawar, police said.
More than 40 other people were wounded in the attack on a bus rented by the government to take staff home after work in the province of Khyber Pakhtunkhwa.
It was the deadliest attack in months on Peshawar, which has long been a flashpoint for Taliban attacks targeting government officials, security forces and civilians.
The city runs into the semi-autonomous tribal belt that US officials consider a safe haven for al-Qaeda and armed groups fighting both in Pakistan and across the border in Afghanistan.
Friday's explosion went off in the Daudzai area, killing government employees and other passengers riding the same bus, officials said.
"The bomb was planted under the bus," provincial information minister Mian Iftikhar Hussain told reporters.
"We still can't say how many government employees and private passengers were killed, but there were heavy human losses."
At the blast site, the back of the colourfully decorated bus was torn apart, leaving a mass of snarled metal.
The injured, who included two policemen, were moved to Peshawar's Lady Reading Hospital. Local television footage showed locals carrying victims to the hospital in private vehicles.
The attack came one day after a remote-controlled bomb killed at least 15 people outside a madrassa, a religious school, in the southwestern city of Quetta.
Pakistan, a country of 180 million people, sits on the frontline of the US-led war on al-Qaeda and since July 2007 has been gripped by local Taliban-led attacks, concentrated largely in the northwest.
In the last five years, attacks blamed on armed groups have killed more than 5,000 people according to a tally by the AFP news agency.
Pakistan's relations with Washington are in disarray, and for the last six months, since US air strikes killed 24 Pakistani soldiers along the border, Islamabad has imposed a blockade on NATO supplies crossing overland into Afghanistan.
On Thursday, Leon Panetta, the US defence secretary, warned Pakistan that the US was running out of patience over Islamabad's refusal to do more to eliminate safe havens for fighters who attack US troops fighting a 10-year war against the Taliban in Afghanistan.