Algerians on Thursday mourned 257 people killed in a military plane crash the day before, the country's worst-ever aviation catastrophe, with no indication yet of the cause.President Abdelaziz Bouteflika announced three days of national mourning after the plane slammed into a field near the Boufarik airbase 30km south of Algiers shortly after it took off on Wednesday.The aircraft was mostly carrying army personnel and their family members on their way back to their barracks in the country's far south.Flags flew at half mast on public buildings and foreign embassies in the capital on Thursday as government departments observed a minute's silence.There was no announcement regarding funeral arrangements, as many of the victims' bodies had yet to be identified.Several large companies took out advertising space in newspapers to offer condolences to the families of the 10 crew members and 247 passengers who died.Mosques across the country are set to hold prayers of mourning on Friday.The Algerian authorities have announced an investigation into the crash, but so far there has been no details of any findings. The plane, which came down shortly after being refuelled, erupted into flames before it hit the ground, witnesses told AFP. Hundreds of ambulances and dozens of fire trucks with sirens wailing rushed to the scene of the crash, in an uninhabited area where one person was injured on the ground by debris.Firefighters took two hours to extinguish the blaze, Algerian media reported.The Ain Naadja military hospital in Algiers, where the bodies were transported, has set up a psychological support unit for victims' relatives and witnesses of the accident.Several cultural events planned for the coming days were cancelled. 'Tragic!' Images of the plane's burned-out frame dominated the front pages of Algeria's newspapers.Francophone daily Liberte led with the headline "Tragic!", while the official Arabic language paper El Moudjahid quoted Bouteflika calling the accident a "painful test" for the country.Several papers praised the pilot, Smail Doucene, citing witnesses who said he had managed to steer the plane away from nearby homes."The pilot saved hundreds of people from certain death," wrote Arabic-language El Khabar.The Ilyushin IL-76 transport plane was bound for Tindouf in southwest Algeria near the borders with Morocco and Western Sahara.The North African country has suffered a string of military and civilian aviation disasters, but Wednesday's was Algeria's deadliest ever plane crash and the world's fourth costliest in human lives in 20 years.Despite no details emerging on the cause of the disaster, several newspapers underlined the poor state of the Algerian military's ageing aircraft.Several previous accidents were due to "poor maintenance of the military air fleet" said Arabic-language daily El Khabar.Liberte said that "to date... very little if nothing has filtered out regarding investigations" into previous accidentsTwo Algerian military planes collided mid-flight in December 2012 during a training exercise in Tlemcen, in the far west of the country, killing the pilots of both planes.In February 2014, 77 people died when a military plane carrying army personnel and family members crashed between Tamanrasset in southern Algeria and the eastern city of Constantine.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.