Security has been beefed up at Dhaka's Hazrat Shahjalal International Airport following tip-off on subversive activities, the airport director said today.

"We stepped up security from last night," airport Director Capt MK Zakir Hassan told The Daily Star. "We received intelligence from the detectives."

The alarm at the country's top airport came after murders of two foreign nationals and bomb attack on Shia Muslim community's Ashura observation.

As part of measures, vigilance has been strengthened through close circuit cameras and security have been raised at each gate of the airport, the director said.

The airport will be under closer supervision, Capt Zakir said.

The airport alert comes in the backdrop of foreign countries maintaining security alert for their citizens residing in Bangladesh – raised after the first foreigner killing.

Murder of Italian national Cesare Tavella raised the first alarm on September 28, followed by the killing of Japanese Kunio Hoshi five days after.

CTG UNDER TIGHTENED SECURITY

Meanwhile, police has stepped up security through Chittagong city and its key points, said Abdul Jalil Mondal, commissioner of Chittagong Metropolitan Police (CMP).

"The measure has been taken in consideration of the overall situation of the country," he told The Daily Star. "Law enforcers have been told to remain alert everywhere."

The port city's Shah Amanat International Airport has stopped its visitors gallery since last night, the airport's Manager Wing Commander Rezaul Karim said. "It is part of the overall security measures."

Murder of Italian national Cesare Tavella raised the first alarm on September 28, followed by the killing of Japanese Kunio Hoshi five days after.

Four weeks into the murder of Hoshi, three improvised bombs were blasted at Hossaini Dalan in Old Dhaka – at a Shia gathering – where one teenager died and at least 80 others were injured.

Terrorist outfit Islamic State claimed responsibility of all those events, US-based for-profit intelligence agency SITE Intelligence Group said.

No one could be arrested over the incidents until today.