Brussels airport
Passengers leaving Brussels airport after a suspected terror strike on 22 March 2016John Thys/AFP

Armed police are to be deployed to key locations across London and the rest of the UK after explosions occurred at Brussels airport and at the city's Maalbeek Metro station. At least 21 people are now thought to have been killed in the blasts, and transport into and out of the city has been cancelled.

Belgian authorities have responded by sending 225 military personnel to the scene and increasing security across the country. In the UK, the police presence has been increased at Gatwick and Heathrow airports while the Met Police has deployed officers to locations across the capital, including transport hubs and major train stations such as London Bridge, Victoria and Waterloo. Specialist search dogs have also been deployed at key ports including St Pancras and Dover.

Brussels explosions LIVE: Multiple deaths after blasts at Zaventem airport and Maalbeek metro

Assistant Commissioner Mark Rowley, the national lead for Counter Terrorism Policing, said the measure was to reassure the public.

"Our thoughts are with the people of Brussels following this morning's horrific attacks. As a precaution, forces across the UK have increased policing presence at key locations, including transport hubs, to protect the public and provide reassurance. This is not in relation to any specific information or intelligence.

"In London specifically, the Metropolitan Police Service has mobilised additional officers, who will carry out highly visible patrols at key locations around the capital, including the transport network. The number of officers deployed will be regularly assessed. These additional officers are deployed as part of reassurance measures.

"The police presence across London and the rest of the UK is constantly under review. We are in close liaison with the Belgium authorities and will continue to monitor the situation. The threat to the UK from international terrorism remains at severe as it has been since August 2014, meaning an attack is highly likely.

"We urge the public and businesses to be alert but not alarmed, and report anything suspicious to the confidential Anti-Terrorist Hotline on 0800 789 321. In an emergency, always call 999."

The move came after Mayor of London Boris Johnson said there was "no imminent threat" to Londoners and that the increase in presence was to "reassure" and was not intelligence-led. Prime minister David Cameron called an emergency COBRA meeting of his top ministers and security officials in reaction to the bombings after tweeting that he was was "shocked and concerned" by the events in the Belgian capital.

Home Office statement

We have taken steps to intensify our efforts at the UK-Belgian and UK-French border. This includes:

• Enhanced searching of inbound tourist vehicles, additional opening of car boots / transit vans

• A heightened Border Force presence at ports

• Targeted Border Force presence at specific ports, with additional security checks on some flights

• Specialist search dogs deployed at key ports including St Pancras and Dover