Backgrounder: Major terror attacks worldwide in past two decades

The Somali radical group Al-Shabaab gunmen on Thursday morning attacked the Moi University's College in Kenya's eastern town of Garissa, leaving at least 147 people dead and more than hundred students still missing so far.

The attack was the worst since Kenya sent troops across the border into Somalia in October 2011.

Following are the major terror attacks worldwide in the past two decades.

January 2015 -- Twelve people were killed and 11 others injured when masked gunmen stormed the offices of Charlie Hebdo in Paris on Jan. 7, 2015.

Al-Qaeda in the Arabian Peninsula (AQAP) claimed responsibility later in an video for the rampage at the French newspaper.

April 2014 -- At least 75 people were killed and 215 others injured in an explosion which rocked a large motor park in Nigeria's capital city Abuja on April 14, 2014.

Nigerian officials blamed the explosion on Boko Haram, a sect which has proved to be a major security threat in the West African country since 2009.

September 2013 -- At least 67 people died and 175 others were seriously injured in a four-day siege at the Westgate Shopping mall in Kenya's capital city. The massacre was also carried out by Al-Shabaab fighters.

May 2013 -- A wave of bombing attacks struck war-torn Iraq on May 17, 2013, leaving at least 73 people dead and 148 others wounded.

July 2012 -- More than 100 people died and 200 others were injured in about 30 terror attacks on July 23, 2012, making the day the bloodiest since August 2011.

July 22, 2011 -- Up to 76 people were killed and more than 80 others injured in a bombing in Oslo, Norway, and a shooting rampage on the nearby island of Utoya.

May 2010 -- Bombers and gunmen killed 114 people on May 10, 2010 in a wave of attacks on markets, a textile factory, checkpoints and other sites across Iraq.

October 2009 -- Two suicide bombs tore through downtown Baghdad on Oct. 25, 2009, killing at least 132 people.

November 2008 -- Armed terrorists launched coordinated attacks in Mumbai, India on Nov. 26-27, 2008, killing at least 195 people, including the head of Mumbai's anti-terrorist squad.

October 2007 -- Suicide attacks on a rally of former Pakistani Prime Minister Benazir Bhutto killed 140 people on Oct. 19, 2007. Bhutto, leader of the Pakistan People's Party, survived the attack but died in an explosion in her election rally on Dec. 27.

August 2007 -- Coordinated suicide bomb attacks in northern Iraq killed at least 500 people on Aug. 14, 2007.

April 2007 -- A series of bombings and attacks across Iraq killed more than 230 people on April 18, 2007, and nearly 190 of them died in Baghdad.

November 2006 -- A series of apparently coordinated bombings killed at least 200 people in Sadr city in eastern Iraq on Nov. 23, 2006.

July 2006 -- A series of powerful bombs ripped through crowded commuter trains in Mumbai on July 11, 2006, India, killing at least 190 people.

September 2005 -- Four suicide car bombings rocked the Iraqi capital of Baghdad on Sept. 14, 2005, killing at least 114 people.

July 2005 -- Fifty-six people were killed and more than 700 others injured by exlosions in London underground trains and a bus on July 7 and July 21, 2005.

February 2005 -- Some 125 people were killed in a suicide car bomb attack in the Iraqi city of Hilla on Feb. 28, 2005.

September 2004 -- At least 333 people died at a school in the town of Beslan of North Ossetia in Russia on Sept. 1, 2004, when more than 1,000 people were taken hostage by terrorists.

August 2004 -- On Aug. 24, 2004, two passenger planes on domestic flights were simultaneously blown up mid-air, killing a total of 90 passengers and crew. Both planes took off from Moscow's Domodedovo airport.

March 2004 -- At least 198 people were killed on March 11, 2004 in commuter train bombings in Madrid, Spain.

March 2004 -- On March 2, 2004, a total of 271 people were killed in a series of terrorist explosions in two mosques of Iraqi Shi'ite Muslims in Baghdad and Karbala.

August 2003 -- Two car bombs detonated outside the Imam Ali Mosque in Najaf, Iraq killed over 100 people on Aug. 29, 2003, including Ayatollah Mohammed Baqir al-Hakim, a Shi'ite spiritual leader.

Oct. 23, 2002 -- Chechen rebels seized a Moscow theater and took about 800 people hostage. 120 of whom were killed.

Oct. 12, 2002 -- A series of bombings targeting foreign tourists on the Indonesian island of Bali killed 202 people.

August 1998 -- A bomb blast, aimed at the U.S. embassy in a busy commercial area in the Kenyan capital, claimed more than 250 lives and injured nearly 5,000 people on Aug. 7, 1998. Endi