KABUL (AFP) - Afghanistan's parliament Monday summoned national security leaders for questioning over an attack at a parade that killed three people, including an MP, although President Hamid Karzai survived. The interior and defence ministers and the national intelligence chief were to be questioned Tuesday about the security measures around the attack on Sunday, parliament said in a statement. A commission was meanwhile investigating the incident, in which militants fired at a stage seating Karzai and a host of cabinet members and foreign diplomats gathered for the country's largest annual parade. Bullets fired into the stage killed a tribal leader. About a dozen people were wounded, including a parliamentarian who died later. A 10-year-old boy was killed when security forces returned fire. Karzai fled for his life, appearing later on television to assure the country the situation was under control. The extremist Taliban said it had carried out the attack, in which three militants were also killed. That the gunmen were able to position themselves about 500 metres from the stage has raised questions about security measures for the event. A number of people arrested Sunday were still being questioned Monday, interior ministry spokesman Zemarai Bashary told AFP. "For the time being, we can't say who was responsible and who did not do a good job that resulted in this incident," he said. At the scene of the incident, in front of the city's largest mosque, security forces were Monday inspecting the cordoned-off stage and guarding a shabby hotel from where the militants opened fire with machine guns and grenade launchers. Meanwhile the White House said it was concerned by the attack, the latest in a series of near misses for Karzai, the first leader of Afghanistan after the fall of the 1996-2001 Taliban regime. The "terrorist threat is real, it is deadly, and defeating this enemy has to be a top priority," said White House spokeswoman Dana Perino.