Bribery and negligence by officials helped Chechen suicide bombers board two passenger planes last month and blow them up, Russia's chief prosecutor said in an interview published Wednesday. The bombers were initially detained by police after arriving at the airport, but were then released without being checked, he said.

Ninety people were killed when the two planes crashed nearly simultaneously on Aug. 24, the start of a wave of attacks in Russia attributed to Chechen separatists.

A week later, a suicide bombing outside a Moscow subway station killed 10. That was followed by the school siege in southern Russia in which at least 338 people were killed, about half of them children.

Investigators on Wednesday confirmed that the planes, which took off from Moscow's Domodedovo International Airport, had been destroyed in midair by explosions on board. Prosecutor General Vladimir Ustinov drew a picture of security negligence that led to the air crashes.

In an interview published by the Interfax news agency and posted on the Web site of the government daily newspaper Rossiiskaya Gazeta, he said two Chechen women blamed for the blasts and their companions had been detained by a police patrol soon after arriving at the airport from the southern town of Makhachkala, near Chechnya.

"The patrol identified them" as suspicious persons, then "withdrew their passports and handed [them] over to the officer in charge of counterterrorism in the airport," Ustinov said. "But the captain let them go without any checks, and the group started hastily trying to buy air tickets in the same airport building."

Ustinov said they later paid 5,000 rubles (about $170) to a black market dealer, who sold them tickets for the flights and helped at least one of them to bribe her way onto the plane, bypassing security checks.

President Vladimir Putin on Monday gave his government two weeks to work out tough measures to tighten up security across the nation.

Ustinov said official negligence and corruption had become a major threat to national security. "We recently checked how regional officials adhere to anti-corruption laws. . . . Almost everywhere, officials are involved in commercial activities, occupy executive posts in different structures, abuse their powers in other ways," he said.