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Dubai, Jan 8: A Ukrainian airliner crashed soon after taking off from Tehran's Imam Khomeini airport on Wednesday, killing all 176 people aboard, Iran's state television and Ukraine's leaders said.

The Boeing 737 belonging to Ukraine International Airlines crashed near the airport and burst into flames. Ukraine's embassy in Iran, citing preliminary information, said the plane had suffered engine failure and the crash was not caused by "terrorism".

Ukraine President Volodymyr Zelenskiy said there were no survivors.

"My sincere condolences to the relatives and friends of all passengers and crew," Zelenskiy said in a statement, adding that Ukraine was seeking to establish the circumstances of the crash and the death toll.

Iranian TV said the crash was due to technical problems but did not elaborate. State broadcaster IRIB said on its website that one of the plane's two black boxes - the flight data recorder and the cockpit voice recorder - had been found.

Iranian media quoted an Iranian aviation official as saying the pilot of the airliner did not declare an emergency.

There was no official word from Ukraine International Airlines. It was the Kiev-based airline's first fatal crash.

"The fire is so heavy that we cannot (do) any rescue... we have 22 ambulances, four bus ambulances and a helicopter at the site," Pirhossein Koulivand, head of Iran's emergency services, told Iranian state television.

Ukraine's prime minister and Iranian state TV said 167 passengers and 9 crew were on board. Iranian TV said 32 of those on board were foreigners.

Television footage showed debris and smouldering engine parts strewn across a field, and rescue workers with face masks retrieving bodies of the victims.

According to air tracking service FlightRadar24, the plane that crashed was Flight PS 752 and was flying to Kiev. The plane was three years old and was a Boeing 737-800NG, it said.

The model's twin engines are made by CFM International, a U.S.-French venture co-owned by General Electric and France's Safran.

Modern aircraft are designed and certified to cope with an engine failure shortly after take-off and to fly for extended periods on one engine. However, an uncontained engine failure releasing shrapnel can cause damage to other aircraft systems.

A spokesman for Boeing said the company was aware of media reports of a plane crash in Iran and was gathering more information. The plane manufacturer grounded its 737 MAX fleet in March after two crashes that killed 346 people.

The 737-800 is one of the world's most-flown models with a good safety record and which does not have the software feature implicated in crashes of the 737 MAX.

Under international rules overseen by the United Nations, Iran is responsible for leading the crash investigation.

Ukraine would be involved and the United States would usually be accredited as the country where the Boeing jet was designed and built. France, where the engine maker CFM has half its activities, may also be involved.

There was no immediate word on whether the U.S. National Transportation Safety Board would be involved in the probe amid escalating tensions between the U.S. and Iran. The NTSB usually invites Boeing to give technical advice in such investigations.

Karachi, Jun 29: Four heavily-armed militants attacked the busy Pakistan Stock Exchange on Monday morning, killing four security guards and a police sub-inspector before being shot dead in an exchange of fire, media reports said.

The unidentified militants opened indiscriminate fire and lobbed hand grenades at the main gate of the building as they tried to storm it, Geo News reported.

Police said that all the terrorists have been killed while five persons injured in the attack.

Four security guards and a police sub-inspector were also killed in the attack.

"An unfortunate incident took place at the Pakistan Stock Exchange. They made their way from our parking area and opened fire on everyone," said Abid Ali Habib, Director of Pakistan Stock Exchange.

The firing by militants caused panic among the people in the building.

Sindh province Governor Imran Ismail condemned the incident.

"Strongly condemn the attack on PSX aimed at tarnishing our relentless war on terror. Have instructed the IG & security agencies to ensure that the perpetrators are caught alive & their handlers are accorded exemplary punishments. We shall protect Sindh at all costs," he said on Twitter.

Police and rangers have arrived on the spot and surrounded the area.

London, May 20: The current physical distancing guidelines of 6 feet may be insufficient to prevent COVID-19 transmission, according to a study which says a mild cough in low wind speeds can propel saliva droplets by as much as 18 feet.

Researchers, including those from the University of Nicosia in Cyprus, said a good baseline for studying the airborne transmission of viruses, like the one behind the COVID-19 pandemic, is a deeper understanding of how particles travel through the air when people cough.

In the study, published in the journal Physics of Fluids, they said even with a slight breeze of about four kilometres per hour (kph), saliva travels 18 feet in 5 seconds.

"The droplet cloud will affect both adults and children of different heights," said study co-author Dimitris Drikakis from the University of Nicosia.

According to the scientists, shorter adults and children could be at higher risk if they are located within the trajectory of the saliva droplets.

They said saliva is a complex fluid, which travels suspended in a bulk of surrounding air released by a cough, adding that many factors affect how saliva droplets travel in the air.

These factors, the study noted, include the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.

In the study, the scientists created a computer simulation to examine the state of every saliva droplet moving through the air in front of a coughing person.

The model considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate, along with a grid representing the space in front of a coughing person.

Each grid, the scientists said, holds information about variables like pressure, fluid velocity, temperature, droplet mass, and droplet position.

The study analysed the fates of nearly 1,008 simulated saliva droplets, and solved as many as 3.7 million equations.

"The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves," explained Talib Dbouk, another co-author of the study.

However, the researchers added that further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air.

They also believe that indoor environments, especially ones with air conditioning, may significantly affect the particle movement through air.

This work is important since it concerns safety distance guidelines, and advances the understanding of the transmission of airborne diseases, Drikakis said.