Pakistan said on Friday that it had stepped up airport security after Britain foiled alleged plans to blow up US-bound flights, with a number of suspects arrested in Pakistan.
"All the airports have been put on high alert," a senior interior ministry official told the agency, adding that security levels had been raised immediately after the plot was revealed.
Extra armed police stood guard at major airports in Karachi, Islamabad and Lahore while passengers were subject to hand baggage restrictions and extra screening, the official said.
Vehicles entering airport car parks were being thoroughly checked.
Pakistan, a key US ally, is already on alert for its Independence Day celebrations early next week.
Pakistani authorities said on Thursday night they had made several arrests, including at least three people linked to Al-Qaeda, which helped Britain uncover the airline bomb plot.