MOSCOW (Reuters) - Russian security services increased patrols and surveillance at military bases, oil pipelines and the Moscow metro on Wednesday after the country's spy chief warned of a potential attack.
The warning came from foreign intelligence services, security officials said. They said they had found no evidence to confirm that an attack was imminent but that the heightened alert would stay in force for now.
Separatists from Russia's Chechnya region have caused huge bloodshed in past attacks but analysts said the most likely threat now was from Islamist militants who share the same ideology and methods as counterparts in Iraq and Afghanistan.
"This is very serious," Moscow-based security analyst Pavel Felgenhauer said. "Officials are thinking that another Madrid or London could happen here."
Islamist bombers killed hundreds of people on the public transport networks in Madrid in 2004 and London in 2005, and analysts say they could now try to seek revenge against Russia for trying to stamp out a separatist war in Muslim Chechnya.
Chechen rebels have hit Moscow before. In 2002 rebels hijacked a central Moscow theatre and 129 hostages died when Russian special forces stormed the building. Two years later bombs on the metro killed dozens of passengers.
After spy chief Nikolai Patrushev's warning on Tuesday Russian officials rushed to assure the public that security had been tightened.
"Moscow mayor Yuri Luzhkov immediately issued instructions .. to step up security," the Moscow mayor's office said in a statement.
Defence Minister Sergei Ivanov said troops would help protect government offices and other potential targets.
Russia's three big mobile telephone operators said at the government's request they had switched off transmitters which allow commuters to use their phones in metro stations.
Patrushev had emphasised foreign intelligence formed the warning's basis, which could be a subtle nod the information came from a country also dealing with Islamist extremism, Felgenhauer said.
"We know that Islamic cells are connected internationally and communicate with each other," he said.
But around 20 hours into the alert, Russia's state anti-terror committee said no evidence could be found to support the foreign information.
"At this time we have not found anything to confirm the information received from our foreign colleagues," Nikolai Sintsov, a spokesman for the national anti-terrorism committee, told Russia's Vesti 24 television.
"As a result of the measures we have taken, the threat of a terrorist act being carried out on overland transport or on the metro has been reduced to a minimum."
"We should note that the operation of our agencies and measures on a heightened status continues," he said.
Overt fighting between Russian forces and Chechen rebels has subsided over the last few months, and Russia's allies in Chechnya said a six-month amnesty which expired on Monday had terminally weakened the separatists.
Last year Aslan Maskhadov, the separatists' president, and Shamil Basayev, their most feared warlord and Russia's most wanted man, were both killed. Basayev organised the 2004 Beslan school siege when more than 300 people died.
Analyst Alexei Malashenko of the Carnegie centre said a hard core of determined Islamic fundamentalists in Chechnya and the neighbouring provinces of Ingushetia and Dagestan were as strong as ever.
"There is an idea expressed by experts that we will face a new generation of political Islamists and radicals," he said.
Russian news agencies report almost daily violence from Ingushetia and Dagestan, which has increased in both ferocity and frequency over the last few months.
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