The young woman was smiling and waving as she approached the bus that had stopped at a railroad crossing near the Caucasus town of Mozdok, North Ossetia.
When the driver refused to open the doors, she tried to lunge beneath the vehicle. Witnesses said she screamed "Allahu akhbar" (God is great).
Then came an explosion that killed at least 17 people, mostly military personnel headed to work at Prokhladny Air Force base, the main base for Russian operations in the neighboring breakaway republic of Chechnya.
It was the third deadly suicide bombing in or around Chechnya in less than a month - and the third to involve Chechen women - a trend presenting a new problem for the Kremlin as it tries to impose peace in Chechnya.
Experts say the unprecedented prominence of female suicide bombers is a sign of Chechen desperation that could signal the "Palestinization" of the mainly Muslim republic's long war of independence from Russia.
"Something has come unglued at the very heart of Chechen society," says Irina Zvigeskaya, an expert with the official Institute of Oriental Studies in Moscow. "It is almost unheard of for Chechen women to fight. They are traditionally the heads of the household and the peacemakers in Chechen society. Many things must have changed irrevocably for Chechen men to accept this terrible new role for women in battle."
At least one woman was with a suicide squad that blew up a Chechen government compound in Znamenskoye May 12, killing 59 people. Days later two female shakhidy, or martyrs, wearing explosive belts, tried to assassinate Chechnya's Moscow-appointed leader, Akhmad Kadyrov, during a religious festival near the Chechen capital of Grozny. Both women, and 15 other people, died..
Last Thursday's attack on the Air Force bus suggests that the appearance of female bombers is no temporary aberration.
"In our culture, both suicide and women joining in combat are unthinkable," says Zainap Gasheyeva, a Chechen and cochair of Ekho Voini, an antiwar coalition of Chechen and Russian women. "But Chechen women who have lost all their menfolk and all their reasons for living may see no other way out. The fact that they attack Russian targets shows who they blame for the destruction of everything that matters to them."
The Kremlin alleges that the deadly wave of what it calls "black widows" is an artificial import into Chechnya by other terrorist groups, who it claims now control the Chechen rebel movement. "All these terrorist attacks are links in a single chain which originates beyond our borders," said Russian Prosecutor General Vladimir Ustinov after the Mozdok blast.
Few deny that there have been outside influences at work in Chechnya. Russian officials and international terror experts say that Al Qaeda has extended its reach to the Caucasus republic. But most observers say that, at least so far, Chechens have not signed on to the worldwide jihad vision of Al Qaeda, but are locked in a localized struggle over land, ethnicity, and independence more like the struggles of Palestinian militants against Israel.
"As in Palestine, we see more and more segments of the population, including women and children, being recruited into terrorism," says Alexander Iskanderyan, head of the Armenia-based Center for Caucasian studies.
A handful of young Palestinian women carried out four suicide bombings in Israel last year, and last month a bomber blew herself up at an Israeli mall. While the number of Middle Eastern female suicide bombers over the years is small, recent intelligence has the FBI worried that even all-male Al Qaeda may be actively recruiting and training women to carry out terror attacks as a way of regaining an element of surprise.
Chechens have been in rebellion against Russia, off and on, for almost two centuries. Two post-Soviet wars killed at least 100,000 people. Human rights workers say that at least 100 Chechens still disappear each month during Russian security operations in the republic.
Three years ago, a woman drove a truck bomb into a Russian military compound near Grozny, killing herself and 17 soldiers. But few tried to emulate her, until about two dozen women took part in the seizure of about 800 hostages in a Moscow theater last October. The siege ended when Russian officers stormed the building, inadvertently killing 129 of the hostages with an experimental knockout gas.
Questions linger over why Russian forces executed all of the Chechens on the spot, even though the gas had rendered them unconscious. "It makes no sense from a police point of view not to capture the culprits and interrogate them," says Ms. Gasheyeva. "But I believe our authorities did not want those women to ever tell their stories in a courtroom or anywhere else. They were killed to shut them up about the horrors that led them to commit such an act of despair."
Surviving hostages confirm that their female captors spoke of ruined lives and personal agony. "The shakhid woman sitting next to me said her brother was killed last year and she lost her husband six months ago," recalls accountant Alla Illyichenko. "She said: 'I have nothing to lose, I have nobody left. So I'll go all the way with this, even though I don't think it's the right thing to do."
"I know of Chechen women who have lost their families and wanted to fight back," says Svetlana Aliyeva, an independent expert who was previously head of the Association of Repressed Peoples of the Caucasus, a human rights group. "But when they tried to join guerrilla units, the men refused them. So they were drawn into the shakhid movement, which offered them a way to fight."
Anna Politkovskaya, a Russian journalist who has covered the Chechnya war, says the Kremlin-backed peace process, which included adoption of a republican constitution by referendum in March, has failed to ease the desperation felt by many Chechen women.
"Human rights are not protected at all in Chechnya," she says. "Before the referendum, people were promised that if they voted for the new constitution, their relatives who had been seized in security sweeps would be returned to them. But nothing of the kind has happened; I don't know of a single case."
• Material from the Associated Press was used in this report.