All flights in Pakistan have been suspended after a string of bomb warnings at airports across the country.

The country’s civil aviation authority is said to have instituted a state of emergency.

Benazir Bhutto International Airport has been evacuated after a phone call saying the building would be blown up.

Sky’s Asia correspondent Alex Crawford said there had been at least two separate threats, and the country was in a state of “high anxiety”.

She said the first threat came in a call to Pakistan International Airline’s call centre.

The second threat was made to the media warning of attacks at airports across the country.

Earlier, the group claiming responsibility for a bomb attack on the Marriott Hotel in the capital warned of more attacks.

Saturday’s truck bombing left 53 people dead and more than 260 wounded.

Security has deteriorated alarmingly in recent months with the government attacking al Qaeda and Taliban strongholds in the north-west.

The militants have retaliated with a string of bomb attacks.

In the latest bloodshed, Pakistani security forces killed 25 Islamists in Bajaur’s Tang Khata area, on the Afghan border.

The Frontier Corps paramilitary force said it had “routed” the fighters, and wounded many more. It gave no information about casualties on the government side.

Relations have soured between the US and Pakistan over the conflict.

Pakistan is under intense pressure to eliminate militant camps in lawless Pashtun regions.

The US has stepped up its attacks on Taliban and al Qaeda fighters in the country. But Pakistan says it is a violation of its sovereignty.