Bloody assaults at two New Zealand mosques that left at least 40 people dead are the latest in a series of attacks on civilians by extremists around the world.
Here is a rundown of some of the most serious since 2015.
A terror attack on a luxury hotel in the Kenyan capital Nairobi claims 14 lives. The attack was claimed by the Al-Qaeda-linked Somali group Al-Shabaab.
A 28-year-old former US Marine kills 12 people in a crowded California country music bar.
A gunman opens fire at the Tree of Life synagogue in the northeastern city of Pittsburgh on October 27, 2018, killing 11 people. He reportedly yelled "All Jews must die!" during the attack.
A former student opens fire at a high school in Parkland, Florida, on February 14, 2018, killing 15 people on the premises. Two others died in hospital.
An Islamic State (IS) group gunman kills nine people in an attack on a church in a south Cairo suburb.
A gunman opens fire with an assault rifle during a Sunday morning church service in the rural Texan community of Sutherland Springs on November 5, 2017, killing 26 people and wounding 20.
A heavily armed "lone wolf" gunman opens fire from a 32-floor hotel room on an open-air concert on the Las Vegas Strip. He kills 58 people before turning the gun on himself. Around 500 are wounded. The IS group claims the gunman but the FBI says it finds no such connection.
A 22-year-old Moroccan man mows down pedestrians with a van on Barcelona's most famous street, Las Ramblas, killing 14 people. The IS group says its "soldiers" carried out the attack.
A van rams into a crowd on London Bridge in the British capital and three assailants attack passers-by. Eight people are killed and around 50 wounded.
A bombing at a pop concert by US star Ariana Grande in the British city of Manchester kills 22 people, including children. Islamist extremists again claim responsibility.
A truck ploughs into shoppers outside a busy department store in central Stockholm, killing five people.
Two churches are bombed on Palm Sunday in Egypt, killing 45 people. The IS group claims responsibility and says both were suicide attacks.
Five people die when a man rams his car into pedestrians on Westminster Bridge in London and then fatally stabs a police officer outside parliament.
A 29-year-old called Alexandre Bissonnette shoots dead six worshippers at a Quebec City mosque.
A Tunisian man hijacks a truck and ploughs into shoppers at a Christmas market in Berlin, killing 12 people. The rampage is claimed by the IS group.
A suicide attack during a Sunday service at a church in central Cairo kills 29. It is claimed by Islamists.
On France's July 14 national holiday a man rams a truck into a crowd in the Mediterranean resort of Nice, killing 86 people. The IS group claims responsibility.
A 29-year-old gunman opens fire inside a gay nightclub in the Florida city of Orlando and kills 49 people. The shooter pledges allegiance to the IS group in a 911 call during the attack.
148 people are killed at Garissa University in northeastern Kenya in an attack claimed by Al-Shabaab insurgents.
Suicide bombings claimed by the IS group kill 32 people and injure 340 more at Brussels airport and the Maelbeek metro station.
At least 14 civilians are killed when gunmen storm the Ivorian beach resort of Grand-Bassam. Al-Qaeda's North African affiliate, Al-Qaeda in the Islamic Maghreb (AQIM), claims responsibility.
Thirty people are killed in an attack on a top Burkina Faso hotel and a nearby restaurant in the capital Ouagadougou. AQIM claims the assault.
A newlywed radicalised Muslim couple storm a Christmas office party at a social services centre in San Bernardino, California and gun down 14 people.
France suffers its worst terror attacks when 130 people die in a string of bombings and shootings at the Bataclan concert hall and several bars and restaurants in Paris, and at the Stade de France stadium. The IS group claims responsibility.
Gunmen take guests and staff hostage at the luxury Radisson Blu hotel in Mali's capital Bamako, in a siege that leaves at least 20 dead. The attack is later claimed by AQIM.
Gunmen kill 21 tourists and a policeman at the Bardo Museum in Tunis, in another attack claimed by the IS group.
In France's first jihadist attack, two brothers who vowed allegiance to Al-Qaeda gun down 12 people at the satirical weekly Charlie Hebdo in Paris. The next day a man linked to the IS group kills a policewoman in a Paris suburb. He takes hostages at a Jewish supermarket the following day, killing four more.