At least 40 people were killed and 35 wounded on Monday when suicide bombers detonated explosives on two packed Moscow metro trains during the morning rush hour, the worst attack in the Russian capital for six years, officials said. No group immediately claimed responsibility for the blasts but suspicion was likely to fall on groups from Russia's North Caucasus, where the Kremlin is fighting a growing Islamist insurgency. According to media reports, the first blast just before 8 am (12.00 am ET) tore through the second carriage of a train as it stood at the Lubyanka metro station, close to the headquarters of Russia's main domestic security service FSB. It killed at least 23 people. Another blast about 40 minutes later wrecked the second carriage of a train waiting at the Park Kultury metro station, killing 14 more people. "Two female terrorist suicide bombers carried out these bombings," Moscow Mayor Yuri Luzhkov told reporters at Park Kultury metro station. Surveillance camera footage posted on the Internet showed motionless bodies lying in Lubyanka station lobby and emergency workers treating victims. The Russian rouble fell to 34.25 from 34.13 against the central bank's euro-dollar basket. Russian equity markets opened down 0.15 percent. Russian prosecutors said they had opened an investigation. Russian Prime Minister Vladimir Putin was being updated regularly on developments, a spokesman said. The current death toll makes it the worst attack on Moscow since February 2004, when a suicide bombing killed at least 39 people and wounded more than 100 on a metro train. Chechen separatists were blamed for that attack. Recent attacks in Russia 1994-1996 - Tens of thousands of people are killed in the first Chechen war. June 1995 - Chechen rebels seize hundreds of hostages in a hospital in the southern Russian town of Budennovsk. More than 100 people are killed during the rebel assault and a botched Russian commando raid. Jan 1996 - Chechen fighters take hundreds hostage in a hospital at Kizlyar in Dagestan, then move them by bus to Pervomaiskoye on the Chechen border. Most rebels escape but many hostages are killed when Russian forces attempt a rescue. Sept 1999 - Bombs destroy apartment blocks in Moscow, Buynaksk and Volgodonsk. More than 200 people are killed. Moscow blames Chechens who in turn blame Russian secret services. Aug-Sept 1999 - Hundreds of Russian soldiers killed battling Chechen militants in the mountains of Dagestan. The second Chechen war begins and Russia bombs Chechnya. Tens of thousands are killed in the war. Russia re-establishes direct rule in 2000. Oct 23-26, 2002 - 129 hostages and 41 Chechen guerrillas are killed when Russian troops storm a Moscow theatre where rebels had taken 700 people captive three days earlier. Most of the hostages are killed by gas used to knock out the Chechens. July 5, 2003 - Two women suicide bombers kill 15 other people when they blow themselves up at an open-air rock festival at Moscow's Tushino airfield. Sixty are injured. Aug 1, 2003 - A suicide bomber driving a truck packed with explosives blows up a military hospital at Mozdok in North Ossetia bordering Chechnya. The blast kills at least 50. Dec 5, 2003 - An explosion tears through a morning commuter train just outside Yessentuki station in Russia's southern fringe. Forty-six people are killed and 160 injured. Dec 9, 2003 - A suicide bomber kills five other people near the Kremlin. At least 13 people are wounded. Feb 6, 2004 - A suicide bombing kills at least 39 people and wounds more than 100 on an underground train in Moscow. May 9, 2004 - Chechen leader Akhmad Kadyrov is killed in a bomb blast in Grozny. June 22, 2004 - Rebels seize an interior ministry building in Ingushetia, near Chechnya, and attack other points in lightning attacks. At least 92 people are killed including the acting regional interior minister, Abukar Kostoyev. Aug 24, 2004 - Two Russian passenger planes are blown up almost simultaneously, killing 90 people. One Tu-134, flying to Volgograd, goes down south of Moscow. Moments later a Tu-154 bound for Sochi crashes near Rostov-on-Don. Aug 31, 2004 - A suicide bomb attack in central Moscow kills 10 people and injures 51. Sept 1-3, 2004 - 331 hostages - half of them children - die in a chaotic storming of School No.1 in Beslan, after it is seized by rebels demanding Chechen independence. Oct 13, 2005 - Up to 100 rebels attack key security points in Nalchik, main city of the Muslim Kabardino-Balkaria region. Twelve local residents are killed as well as 12 police. Twenty fighters are killed and 12 are seized by security forces. Feb 10, 2006 - Seven Russian policemen and 12 gunmen are killed when special forces storm houses to fight rebels holed up in a village in the Stavropol region of southern Russia. Aug 21, 2006 - A bomb kills 10 people in a Moscow suburban market. April 27, 2007 - A Russian helicopter is shot down in Chechnya, killing 18 people. Aug 13, 2007 - A bomb derails the Nevsky Express between Moscow and St Petersburg, injuring 60 people. Aug 31, 2007 - A bomb on a bus in the Southern Russian city of Togliatti kills eight and injures 50 during the rush hour. June 22, 2009 - Ingush President Yunus-Bek Yevkurov is seriously injured when a suicide bomber detonates explosives beside his car. He later recovers and returns to work. Aug 17, 2009 - A suicide bomber drives a truck into the gates of the main police station in Nazran, the largest city in Ingushetia, killing 20 people and wounding 138 others. Nov 27, 2009 - A bomb blast derails the Nevsky Express with about 700 people on board. At least 26 people are killed and 100 injured. Jan 6, 2010 - At least seven policemen are killed and 20 more injured in Dagestan when a suicide bomber detonates a car packed with explosives at a traffic police depot. March 29, 2010 - At least two blasts strike Moscow metro stations during rush hour, killing 34 people and wounding 18.