The Belgian federal prosecutor Fredere Van Leeuw has confirmed that the three explosions this morning - two at Brussels Airport and one in the subway station Maelbeek - were terror attacks.

The anti-terror section of the federal prosecutor’s office has opened a criminal investigation, the prosecutor's office said.

The Belgian Prime Minister, Charles Michel, has just given a press conference. He confirmed that there were two attacks in Brussels this morning - one at Zaventem airport and the other at Maelbeek metro station.

Mr Michel said many people were killed and many wounded.  

He confirmed that the airport attack was carried out by a suicide bomber. 

He said authorities were evaluating the threat and that additional security measures were being put in place, including military enforcements over border control.

Reports on the death toll have varied. A spokesman for the Brussels fire brigade earlier told the AFP news agency that 21 people had died.

French newspaper Le Soir reports that a number of small blasts heard on the Rue de la Loi, the location of Maelbeek metro station, were part of a controlled explosion of a suspect package.

Footage taken outside Maelbeek station earlier shows people being treated following the explosion at the station. 

An extra 1,600 police will be deployed around France to stations, airports and borders, Interior Minister Bernard Cazeneuve said in a statement. 

Similar precautions have been taken in London and New York.

Mark Rowley, the Metropolitan police counter-terrorism chief, said in statement that additional security had been deployed as a precaution.

"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."

BBC Monitoring

There has been no jihadist claim of responsibility yet for the airport and metro explosions in Brussels today. However, online supporters of Islamic State group (IS) have praised the blasts and appear to believe that IS was responsible for them.

Some have used the Arabic-language hashtag "#Brusselsonfire" to praise the events. IS supporters have in the past used similarly-worded hashtags to celebrate IS attacks, such as "#Parisonfire" to celebrate IS's 13 November attacks in Paris.

If IS is indeed behind the Brussels bombings, it is likely to delay claming responsibility until the operation has been concluded: i.e. that no further attacks are planned and/or its operatives are all dead or have escaped.

By contrast, al-Qaeda supporters on Twitter have not been been active in posting about the attacks, largely flagging mainstream media reports instead.

The BBC's Sofia Bettiza captured footage of emergency teams arriving at Maalbeek metro station following the blast there earlier this morning.

At least 21 people have died in the attacks on Brussels airport and metro system, Pierre Meys, a spokesman for the Brussels fire brigade, has told AFP.

Mr Meys said 11 people were killed in the twin blasts at the airport.  

A passenger who was near Maalbeek station describes the moment of the blast.

BBC Monitoring

Russian President Vladimir Putin has condemned what he called "barbaric acts" in Brussels, Russian news agency Interfax reports, quoting his press secretary Dmitry Peskov. 

"The president resolutely condemned these barbaric acts, expressed his condolences to the Belgian people and assured King Philippe of absolute solidarity with the Belgians in these difficult hours," Mr Peskov said.

Speaking live on state-owned rolling news channel Rossiya 24, Russian Foreign Ministry spokesperson Maria Zakharova said: "As more and more time and lives are lost, people are beginning to understand that this policy of double standards in evaluating terrorist activities is a dead-end policy." 

Frank Gardner
BBC Security Correspondent

BBC security correspondent Frank Gardner says it is "not a surprise" that this attack has taken place but says it is "shocking it was so successful". 

He said since the Since Charlie Hebo attacks in Paris in January last year, which killed 12 people, there had been a number of terror cells "on the loose" that had been inspired by so-called Islamic State and had access to weapons and explosives. 

He said Belgian intelligence services had been playing "catch-up" since then and did not have a "very good system" of sharing information across the various authorities.

He said attacks in Britain had been prevented by Muslim communities reporting suspicious behaviour to police but this was not yet happening in Belgium. 

An eyewitness speaks to BBC News about the airport bombing.

A passenger on the Brussels metro captured video footage of people walking along the tracks after trains were evacuated in the tunnels. 

The city's metro system has been completely shut down following at least one blast, at Maalbeek station in central Brussels.

Belgian broadcaster RTBF says the federal prosecutor in the case has confirmed that the airport explosion was a suicide attack, external.

Eurostar, which tweeted earlier to say its trains were still running, has now cancelled services in and out of Brussels Midi.

Martin Schultz, president of the European Parliament, has tweeted to offer condolences and condemn the attacks. 

The crisis centre is also advising people to text or use social media rather than call.

EU official Kristalina Georgieva says alert level for Brussels institutions has been raised to orange.

The first set of explosions took place at around 08:00 (07:00 GMT) at Zaventum airport.

Some time later, a blast was reported at Maalbeek metro station, close to the city's EU buildings.