Grieving relatives in the town of Beslan in southern Russia continue to search for the remains of those who died Friday, when Russian troops stormed the school where more than 1,000 people were held hostage by terrorists. At least 350 people, half of them children, died in Russia's deadliest act of terror. President Vladimir Putin says security will be tightened in the wake of the massacre.

Many of the residents of Beslan have been unable to locate their missing children or relatives two days after the chaotic storming of the school, when hundreds of hostages managed to escape in the middle of a fierce gun battle.

Many people were burned beyond recognition in the school gymnasium after the roof collapsed when the militants who seized the school on its opening day set off explosives under it.

Security officials also say the militants managed to stockpile weapons and explosives inside the school by posing as workmen reconstructing the building in recent weeks.

Late Saturday, President Putin spoke about the tragedy in a televised address, saying that Russia would never give in to blackmail and calling for all Russians to join in the fight against terrorism.

He acknowledged that security measures were inadequate and made the country vulnerable.

"We have showed weakness in the face of danger," he said, "and the weak get beaten up." The Russian leader said new measures to tighten security will soon be put in place.

Security officials in southern Russia say that many of the 26 militants who seized the school were foreign mercenaries, mostly from Arab countries. This has not been independently confirmed, but President Putin has been citing the presence of foreign enemies of Russia among the reasons for his tough stand against separatists in Chechnya.

Many analysts say this hard-line policy is encouraging more extremism among Chechens, and attracting hard-core Islamic militants to join them.

But Mr. Putin gave no signal of softening his uncompromising position on Chechnya, and he has consistently rejected calls from Western leaders to seek a political solution to the decade-long Chechen conflict.