The attacks in Brussels are the latest in a long line of atrocities linked to Islamic terrorism since the turn of the century.
The co-ordinated bombings of the airport and a Metro station in the Belgian capital follow the arrest of key Paris attacks suspect Salah Abdeslam in the city just days earlier.
Here are some of the most horrific attacks:
9/11
Nearly 3,000 people, including 67 Britons, were killed when Islamist extremists hijacked passenger jets and flew them into New York's World Trade Centre twin towers and the Pentagon in Washington DC on September 11 2001.
The 9/11 attacks were meticulously planned by Islamist fanatics to kill as many people and gain as much publicity as possible, with news footage televised live around the globe to a shocked audience of billions.
Bali
A total of 202 people, including 28 Britons, were killed on October 12 2002 and more than 204 injured when the al Qaida-linked Jemaah Islamiyah group detonated bombs at two packed Bali nightspots.
During the attack three bombs detonated - a backpack carried by a suicide bomber and a car bomb which both devastated Paddy's Pub and the Sari Club opposite, followed by a third device outside the US consulate in Denpasar.
Various members of Jemaah Islamiyah were convicted in relation to the bombings. Three - Imam Samudra, Amrozi Nurhasyim and Huda bin Abdul Haq - were executed by firing squad in November 2008.
Madrid train bombings
The whole of Spain was in mourning when more than 190 people were killed in the Madrid train bombs on March 11 2004.
The attacks took place exactly two-and-a-half years after September 11 and were Europe's worst terrorist atrocity since the 1988 Lockerbie plane bombing.
London-based Arabic language newspaper Al Quds said it received an email from the Brigade of Abu Hafs al-Masri, which claimed its "death squad" had penetrated "one of the pillars of the crusader alliance".
7/7
On July 7 2005, 52 people were murdered and hundreds more injured when four suicide bombers attacked London's transport network.
Twenty-six died in the bombing at Russell Square on the Piccadilly line, six in the bombing at Edgware Road on the Circle line, seven in the bombing at Aldgate on the Circle line, and 13 in the bombing on a bus at Tavistock Square.
A fortnight later, another four would-be suicide bombers launched failed attacks on the Tube and a bus, leading police marksmen to kill innocent Brazilian Jean Charles de Menezes.
Mumbai
Often called India's 9/11, the Mumbai attacks in 2008 saw 10 gunmen blaze through the country's financial capital, killing more than 160 people.
Indian authorities took back control of Mumbai early on the morning of November 29 after a three-day siege across the city.
Security services and senior police in the UK have repeatedly highlighted the risk of a Mumbai-style roaming gun massacre, and earlier this year police carried out a simulated terror attack in the capital to test the emergency response to such a strike.
Lee Rigby
Fusilier Lee Rigby, 25, from Middleton in Greater Manchester, was killed outside barracks in Woolwich, south east London, on May 22 2013 by two Islamic extremists.
The murder sparked shock across the country after the father of one was run over with a car and then hacked to death by British Muslim converts Michael Adebolajo and Michael Adebowale.
Following an Old Bailey trial, Adebolajo was handed a whole-life prison term and Adebowale was jailed for a minimum of 45 years.
Charlie Hebdo
Paris was rocked by the Charlie Hebdo atrocity on January 7 last year, when 12 people were killed after gunmen stormed the offices of the satirical magazine.
The sense of panic heightened when there was a subsequent attack on a kosher supermarket, and the incidents triggered worldwide outrage.
Subsequently there were a number of more minor strikes or attempts in France. In one, three Americans and a Briton overpowered a heavily armed gunman on a train from Amsterdam to Paris.
Sousse
Terror group Islamic State claimed responsibility for the Sousse attack in June, in which 30 Britons were among 38 tourists killed.
Gunman Seifeddine Rezgui opened fire on the holidaymakers on a beach in the Tunisian holiday resort.
Foreign minister Tobias Ellwood described the Sousse tragedy as the "most significant terrorist attack" on Britons since July 7 2005.
Paris
Co-ordinated suicide bombings and shootings at cafes, bars, a rock concert and a stadium in the French capital left 130 people dead in the worst terrorist assault on Europe in a decade.
Most of the Paris attackers died on the night of November 13 2015, including Salah Abdeslam's brother Brahim, who blew himself up.
Belgian extremist Abdelhamid Abaaoud, 27, suspected of masterminding the deadly attacks in Paris, died along with his female cousin in a police raid in the Paris suburb of Saint-Denis days later.
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