Another terror attack hits Russia

Local news agency says at least 14 people killed and another 20 wounded after a trolleybus explodes in Volgograd city.

At least 14 people have been killed and 20 wounded in a suicide bomb attack on a packed trolleybus in Russia's Volgograd city, according to the Interfax news agency.

Volgograd was on high alert on Monday following the latest attack, that came a day after a suicide bombing at a train station in the city killed 17 people.

"An explosion in Volgograd trolleybus is likely to be a terror attack, judging from the two previous attacks on a bus and a train station," said an official from the security services who was not named by Interfax.

The National Anti-Terrorism Committee said the trolleybus explosion at about 8:30am local time (0430GMT) was most likely caused by a bomb, but there were no further details.

Al Jazeera's Peter Sharp, reporting from Moscow, said the blast was unlikely to be a suicide attack as preliminary reports suggested the bomb was planted in the middle of the trolleybus.

However, later on Monday Russia's main investigative body suggested a male suicide bomber carried out an attack.

"It is now possible to preliminarily say that the explosive device was set off by a suicide bomber - a man whose body fragments have been collected and sent to genetic testing," the federal Investigative Committee said in a statement.

Russian investigators have opened a criminal probe into a suspected act of terror as well as the illegal carrying of weapons, Investigative Committee spokeman Vladimir Markin told Interfax.

Russian President Vladimir Putin has sent Alexander Bordnikov, director of Federal Security Service, to Volgograd while the Interior Ministry raised the number of its staff in the city.

The ministry was also expected to send a plane to Volgograd for transporting the wounded in Monday's attack to Moscow for medical treatment, according to Interfax.

The attack on Monday was the third on the city in the past three months.

On October 21, a female suicide bomber blew herself up on a bus, killing six people.

The blasts have raised safety concerns in the region ahead of the Winter Olympics 2014 due to take place in February in Sochi, about 650 km southwest of Volgograd.

There was no immediate claim of responsibility for either of the Volgograd attacks, which came several months after Chechen rebel leader Doku Umarov called for new attacks against civilian targets in Russia, including Sochi Games.

In the past, armed groups have carried out attacks in cities beyond the borders of the North Caucasus.

Rebels have said they want to carve out a Muslim state in the North Caucasus. Their insurgency is rooted in two post-Soviet wars in Chechnya, one of the region's provinces.

Putin, who was first elected president in 2000 after launching the second war in Chechnya, which drove Chechen separatists from power, has staked his reputation on a safe and successful Winter Games.

Extracts from Aljazeera