VLADIKAVKAZ, Russia (AP) _ Grieving relatives on Monday buried victims of a suicide truck bombing that killed 50 people in southern Russia, while the region's military leader vowed revenge for the latest in a string of attacks Russian officials blame on Chechen rebels.

Mourners placed flowers before a black memorial stone set before a stark wooden cross at the site of the military hospital destroyed in Friday's attack in the city of Mozdok. Flags flew at half-staff over government buildings in the regional capital, Vladikavkaz. Workers and military units began their day by observing a moment of silence.

In an emotional statement, the chief of the North Caucasus Military District vowed to avenge the victims of the attack, which a spokesman for the Russian Prosecutor General's office in the North Caucasus region said authorities suspect was masterminded by Chechen rebel warlord Shamil Basayev.

``Those who think that they can bring us to our knees with such atrocities are deeply mistaken,'' said Col. Gen. Vladimir Boldyrev, chief of the North Caucasus Military District, his voice choked with emotion. ``We will avenge that, we will destroy the bandits always and everywhere until we have destroyed them all.''

President Vladimir Putin said Saturday the attack would not derail efforts to bring peace to Chechnya and the surrounding region. But while the Kremlin has approved a partial amnesty, a regional presidential election and other steps it says are aimed at a political settlement in Chechnya, it has also pledged to continue fighting rebels.

The attack _ the latest in a series of suicide bombings that have killed more than 150 people since May _ underlined the inability of the authorities to avert bombings of military, government and civilian targets both inside and outside Chechnya that have become a deadly component of Russia's second war in the region in a decade.

Relatives mourned Monday at funerals for victims of the attack, who included soldiers recovering from wounds suffered in Chechnya as well as hospital personnel and civilians.

``You never fought with anyone ... but they came and killed you, let them be cursed forever,'' grieving father Yuri Orlov said at the funeral of his son, Lt. Mikhail Orlov, a military anesthesiologist whose body was retrieved from the rubble Saturday. Orlov was buried in the southern city of Rostov-on-Don.

Lt. Col. Igor Lapin, the head of the hospital's intensive care unit, said Orlov had been in a second-floor operating room when the truck crashed through the hospital gates and exploded, and that he had been crushed by a concrete slab along with a nurse and the patient who was undergoing surgery.

Sixty-four victims of Friday's attack remained hospitalized, many in grave condition, officials said Sunday.

Security was tightened throughout the Northern Caucasus region, which includes North Ossetia, where the attack took place, and Chechnya. Police patrols were placed around hospitals and public facilities and troops sealed off the main military hospital in Vladikavkaz, barring all nonmilitary visitors from entering the building.

Nikolai Patrushev, the chief of the Federal Security Service, the main KGB successor agency, said on a trip to southern Russia that his service had ``general'' information prior to the explosion about a possible attack, but no specifics. He and other officials criticized lax security at the hospital.

Meanwhile, police in the Russian republic of Ingushetia, which is wedged between Chechnya and North Ossetia, said Monday that a powerful radio-controlled explosive device was discovered Sunday in the town of Malgobek. The device was safely defused, Ingushetia police spokeswoman Madina Khadziyeva said.