Prime Minister Sheikh Hasina yesterday instructed the civil aviation authorities to give highest priority to flight safety and maintenance of planes of carriers.

Speaking at a meeting at the Prime Minister's Office (PMO), she said the reasons behind the US-Bangla plane crash in Kathmandu were yet to be known and asked all concerned to stay cautious, according to the PMO.

Hasina had cut short her Singapore trip and returned Tuesday afternoon in the wake of the BS211 disaster.

Immediately after the meeting, the civil aviation and tourism ministry asked all carriers to follow the PM's directives, the standards set by the International Civil Aviation Organisation (ICAO) regarding flight safety and maintenance, a top official of the ministry present at the meeting told The Daily Star.

The official said air-worthy certificates of aircraft would not be renewed if an airlines failed to comply with the directives.

A US-Bangla Airlines Bombardier Dash 8 Q-400 with 71 people onboard slammed on an empty field and burst into flames at the Tribhuvan International Airport on Monday.

At least 51 people, including 28 Bangladeshis, died.

Bangladesh declared national mourning today. The flag will be at half-mast at government offices, educational institutions, and diplomatic missions across the world.

Special prayers will be offered at religious institutions and places of worships across the country tomorrow.

Following the PM's directive, a seven-member medical team, comprising burn and orthopaedic doctors and anaesthesiologists, have also been formed and it would leave for Kathmandu today to help Nepalese doctors treat the survivors.

The team, led by Lutfar Kader Lenin of DMCH burn unit, has a forensic specialist to collect DNA samples of the deceased, Director General Abul Kalam Azad of Directorate General of Health Services told The Daily Star.

However, the team is being sent at a time when the Nepalese authorities are about to send some of the seriously injured to Singapore for better treatment.

Samanta Lal Sen, founder of the burn and plastic surgery unit of DMCH, said Nepal did not have a large burn unit like the DMCH has but they had treatment facilities for burn injuries.

Asked if it was rather late for sending a medical team, he said, “No, it is not late. We have to know the ground realities [in Nepal] before we move. Also, we need permission of the country.”

Bangladesh government sent ministers, and high officials while US-Bangla took relatives of the victims to Kathmandu a day after the crash but no doctor was sent, which many believe was required.

Of the eight Bangladeshi survivors being treated at two hospitals in Kathmandu, the conditions of five are critical and one or two of them could be sent to Singapore, US-Bangla CEO Imran Asif told The Daily Star yesterday.

He said Rezwanul Haque was one who might be sent to Singapore in an air ambulance. He also said conditions of two Bangladeshis were better and they could be sent home today on receipt of no-objection certificates.

A team of civil aviation officials of Nepal and Bangladesh are investigating the crash.

Team leader Yagya Prasad Gautam, former director general of the Civil Aviation Authority of Nepal, said the team collected evidence from the scene and also talked to survivors.

"I also sought some technical documents from Bangladesh authorities for the investigation," he told The Daily Star over telephone.

Identification of all the bodies could not be completed. The Nepalese authorities said it would take several more days before those could be sent back to Bangladesh.

Meanwhile, US-Bangla Airlines has closed its flight operations between Dhaka and Kathmandu for indefinite period.

“Our flight operations between Dhaka and Kathmandu have been shut from today due to shortage of aircraft,” Kamrul Islam, general manager (public relations) of the US-Bangla Airlines, told The Daily Star.