Hundreds of Chechens have been thrown into crowded Moscow police cells this week as a wave of anti-Chechen feeling sweeps the city.
No one has claimed responsibility for the two huge blasts which killed more than 200 Muscovites as they slept, but the government blames extremists from the northern Caucasus.
Yesterday a smaller blast in a St Petersburg block of flats - the fifth in a series of explosions in Russia - heightened the tension, but the police said the bomb, which killed two people, was probably not linked to the others. "This explosion is most likely the result of a criminal settling of accounts," a senior officer said.
In Moscow, detectives detained two Chechens suspected of causing the previous blasts. Timur Dakhkilov, 32, was said to have traces of an explosive on his hands. The same compound was allegedly found in the flat of a relative, Bekmara Sautiyev.
The arrests are part of a security crackdown now striking fear into the 100,000 Chechens living in Moscow.
The knock on Said Lorsanukayev's door came at 2am. When he opened it, two policemen demanded his identity papers. A routine check, they told him.
As a Chechen who has lived for several years in the Russian capital, and is an aide to the speaker of the Russian parliament, he was surprised but not shocked. "I understand the authorities have to find and punish terrorists," he said.
The horror came half an hour later. There was a second knock. This time a group of men in plain clothes stormed into the flat, forced Mr Lorsanukayev's wife and four children out of their beds, and dragged them all off to a police station. They were interrogated until 4am.
"It was humiliating. Do they have to see a bandit in every Chechen? And what are children guilty of?" Mr Lorsanukayev asked angrily.
Chechen community leaders are furious, too. "It was never like this during Russia's war with Chechnya," said Mairbek Vachagayev, the Chechen government's representative in Moscow. "At that time there was some sort of understanding of our case, and even support for it. Now it's like a mass psychosis.
"We're on the receiving end of all the charms of the ancient pogroms against the Jews. I now see what it's like to be an enemy of the people."
Although freedom of movement is enshrined in the Russian constitution, Moscow has never abandoned the Soviet system of requiring people to obtain residence permits.
The mayor, Yuri Luzhkov, announced on Monday that all non-residents would have to re-register immediately. Police and soldiers have been stopping thousands of people on the streets. They concentrate on those of "Caucasian" appearance - or, as the Russians call them, "blacks".
The fact that there is little unity between the scores of nationalities in the Caucasus, let alone among Chechens themselves, is ignored. Russian police have raided several markets, rounding up scores of people, even though most traders are from Azerbaijan, Georgia and Abkhazia.
"They can seize your truck and all its fruit if you don't have the right documents," said Akber Guseinov, a driver from Azerbaijan.
Mr Vachagayev, the Chechen envoy, condemned the terrorist bombings, but said Russia's way of dealing with it was flawed. Air raids on three villages in Chechnya in the past few days have killed more than 200 civilians.
For the moment his main task is to try to protect Chechens in Moscow. "There are 529 Chechens in Moscow cells, most of them picked up in the last few weeks," he said. "We have only managed to get 20 released. They had cast-iron alibis.
"The police can only hold people for three days without charge, but they often plant evidence so that detainees can be convicted."
He produced an affidavit from Amirkhanov Yakubovich, who claimed that the police stopped his car and forced him to drive with his brother to a wood. There they were beaten and told they would be shot. Later, Mr Yakubovich said, the police put bullets into his pocket and a packet into his brother's. They were accused of possessing heroin and illegal firearms.
"Many Chechens have sewn up their pockets to avoid this kind of thing," Mr Vachagayev said.
Some Russians have stood up for the Chechens. Mr Vachagayev cited a woman who saw police arresting a man and putting a packet into his pocket. When she protested, one of the officers shouted, "Shut up. He's a Chechen."
"The woman insisted that she would not allow them to frame him, whoever the man was. The police then let him go. He should give thanks to God. That woman saved three or even five years of his life."