KABUL — The American University of Afghanistan in Kabul came under attack by bomb and gunfire on Wednesday night, in a siege that stretched for hours as pockets of people trapped on campus tried to escape. The Afghan Health Ministry said that a security guard was killed in the attack and that at least 26 people had been wounded. [...] near midnight, though the sounds of gunfire had ebbed, there were still occasional outbursts, and officials said they were still unsure how many attackers might still be alive, and how many people might still be pinned down, hurt or killed. Afghan security forces massed around the campus, a guarded compound in the western part of the capital, after initial reports of an explosion and gunfire. The university opened for enrollment in 2006 to both men and women, and quickly became a prestigious education choice for some of Afghanistan’s elites, offering undergraduate and graduate degrees taught in English. Some who were still in touch with their relatives trapped in the darkness inside expressed frustration that the security forces had not reached them hours after the raid begun.