Media playback is unsupported on your device Media caption Zubeidat Tsarnaeva: "America took my kids away from me"

The mother of the Boston marathon bombings suspect says she regrets that the family emigrated to the US, more than 10 years ago.

At a news conference in the Russian republic of Dagestan, where she now lives, Zubeidat Tsarnaeva said America had taken her children away from her.

She also reiterated she was sure her sons were not involved in the attack.

It is being reported that her elder son was added to a terrorism database 18 months ago at the CIA's request.

Three people were killed and more than 260 wounded when two devices exploded at the Boston marathon on 15 April.

Mother's shoplifting charge

"I would prefer not to have lived in America. Why did I go there?" Mrs Tsarnaeva said at Thursday's news conference in Makhachkala, Dagestan.

Analysis The parents of the two suspected Boston bombers remain convinced that their children are innocent and that they have - for some unknown reason - been framed. The news conference was a chaotic and emotional affair. Zubeidat Tsarnaeva descended into tears as she said she was "sure" her children were not involved. She dismissed the evidence presented so far and denied that her youngest son Dzhokar had told investigators anything. Mrs Tsarnaeva also spoke about an Armenian man called Misha, a convert to Islam who became a family friend back in 2007. She said her elder son Tamerlan had "respected him very much" for his adherence to Islam. But she denied their son had become radicalised after his six month visit in Dagestan last year, saying she saw no change in him on his return.

"I thought America would protect us. America took my kids away from me... I'm sure my kids were not involved in anything."

Her elder son, 26-year-old Tamerlan Tsarnaev, was killed a few days after the bombing during a shootout with police.

His younger brother, Dzhokhar Tsarnaev, 19, was captured and charged in connection with the attack.

The suspects' father, Anzor Tsarnaev, has said he will travel to the US on Thursday or Friday. The family wants to take the dead son's body back to Russia.

Zubeidat Tsarnaeva has said she is still undecided whether to go, AP news agency reports, because she was charged with shoplifting in the US last year and fears arrest if she returns.

In questioning from his hospital bedside, where Dzhokhar Tsarnaev is being treated for gunshot wounds, he has reportedly said he and his brother were angry about the US wars in Iraq and Afghanistan.

'Cowardly jihadis'

In 2012, his older brother spent six months with relatives in Dagestan, which has an Islamist militant insurgency.

But congressmen said on Wednesday after closed-door briefings that the brothers are not believed to have had direct contact with a militant organisation.

In other developments:

The brothers discussed setting off their remaining explosives in New York's Times Square, law enforcement sources have told US media

Dzhokhar Tsarnaev stopped answering questions after investigators read him his legal rights to remain silent, US media also report

Vice-President Joe Biden labelled the suspects "two twisted, perverted, cowardly, knockoff jihadis", at a memorial on Wednesday

Massachusetts officials confirmed that the Tsarnaev family had received welfare benefits

Meanwhile, there are questions as to whether the authorities did enough to prevent the bombings.

Media playback is unsupported on your device Media caption Ballroom dancer Adrianne Haslet, who lost her left foot in the attack, vows to dance again

US media report that Tamerlan Tsarnaev was added in 2011 to the Terrorist Identities Datamart Environment (Tide), at the request of the CIA.

The database contains as many as 745,000 entries; individuals on that list are not necessarily on the so-called terrorist watch list.

The FBI investigated after Russian authorities alerted US counterparts to the activities of Tamerlan Tsarnaev, saying he had become a follower of radical Islam.

About six months before the CIA requested his name be added to Tide, the FBI asked the Russians for more information about the elder brother but received none, and closed its investigation.

US officials said earlier that their intelligence community had no information about threats to the marathon ahead of last week's attacks.

After a classified briefing at the House intelligence committee on Wednesday, Democratic Congressman Dutch Ruppersberger said he believed the FBI was not at fault.