A second bomb in another town in Punjab wounded eight people, the provincial chief minister Mohammad Arif Nakai, said.
Police said earlier that the Lahore explosion, at a food stall outside a domestic departure lounge at the airport, killed six people and wounded more than 50. But Mr Nakai later said that four people were killed and 68 injured by the blast, which he blamed on unidentified "external elements".
There was no immediate claim of responsibility or information about who had set off the bomb, the latest in a series of such attacks in Punjab - the country's most populous province. The attacks have killed 70 people and wounded hundreds more.
A senior police official, who asked not to be named, said he suspected a "foreign hand". In the past, the authorities have accused intelligence networks from India of sponsoring bomb attacks in Punjab in retaliation for Pakistan's support for militants fighting Indian rule in Kashmir. India has denied the charges.
Ms Bhutto, who is visiting South Korea, condemned the Lahore attack in a message which said: "Terrorists are out to terrorise the people and government of Pakistan." State television quoted her as declaring she would not compromise with terrorists and would "deal with them with an iron hand".
Political sources said the bombings were likely to put Ms Bhutto under fresh pressure from opponents who are already accusing the government of failing to maintain the peace or to check corruption.Reuse content