ISTANBUL (AFP) - A teenager from Russia's Muslim region of Dagestan, suspected of a suicide bombing in Istanbul, was said on Friday to have been an Islamic State in Iraq and Syria (ISIS) militant and the widow of an Norwegian extremist.

A policeman and the female suicide bomber were killed in the attack on Jan 6 in Sultanahmet, the heart of Istanbul's tourist district and home to its greatest concentration of historic monuments.

Turkish authorities have so far refrained from naming the suicide bomber but reports in Turkey and Russia Friday identified her as Diana Ramazanova, 18, from the northern Caucasus region of Dagestan.

The Hurriyet daily said she was the widow of Abu Aluevitsj Edelbijev, a Norwegian citizen of Chechen origin.

The pair were married last year in a religious ceremony, either in Istanbul or in Syria.

The report said that Ramazanova had entered Turkey on a tourist visa in May 2014 but Edelbijev may have entered the country illegally.

Last July, the pair crossed the border from Turkey into Syria, joining ISIS militants who have seized large parts of Syria up to the Turkish border.

He took the name of Idris, while she became known as Sumeyra, it said.

Edelbijev was killed in December while fighting. Ramazanova then crossed the border illegally back into Turkey on Dec 26, before carrying out the suicide bombing in Istanbul on Jan 6.

Hurriyet said security services are still trying to ascertain whether she had brought her explosives with her from Syria or whether they had been given to her by a contact in Istanbul.

The family of her late husband has confirmed that Ramazanova was the suicide bomber.

"I don't think she could take it any more. She said that Abu was in peace and that she wanted peace too," Edelbijev's mother told Norwegian TV2.

Edelbijev's mother also told the Norwegian broadcaster NRK that she had spoken with her daughter-in-law the day before the attack.

"We had regular contacts through instant messaging online. Everything seemed normal. We had contacts no later than in the evening of Jan 5. She spoke about her family and sent pictures," she said.

The Edelbijev family had actually never met Ramazanova but had been due to travel to Turkey to meet her last Friday.

"There was nothing that suggested that this could happen. It was as much of a shock for us when she blew herself up as when my son decided to go to Syria. We're struggling now," Edelbijev's mother added.

'LOVED MAKE-UP'

If confirmed, the newspaper's information would make clear for the first time an Islamic militant link to the Istanbul suicide bombing.

It also raises new questions about the laxity of Turkey's border security, which has already been criticised by Western states for allowing extremists in and out of Syria.

A radical outlawed Marxist group had initially caused confusion by claiming the attack but then retracted that claim, saying it had made a mistake.

Both Russian media and Hurriyet published pictures of Ramazanova before she was married, showing a seemingly normal Russian girl who took good care of her appearance and wore short dresses.

Without specifying the source of the images, Hurriyet also published pictures it said were of the pair with fellow militants in Syria.

Russian media have been quick to dub Ramazanova a "black widow", the label given to female suicide bombers from the Caucasus who carried out attacks in Russia after their husbands were killed by the Russian security forces.

Russian newspaper Kommersant reported on Thursday that the local security services in Dagestan also believed Ramazanova had carried out the suicide bombing.

Tabloid news site lifenews.ru cited acquaintances of Ramazanova in Dagestan and Moscow as saying she had totally changed after meeting her extremist husband on a social networking site.

"She was fashionable, a very beautiful girl. She loved to put make-up. I even rebuked her for wearing unsuitable clothes at school," it quoted a Moscow teacher as saying.

Ramazanova's purported page on Russian social network VKontakte, with a profile picture of her eating a cake, gives her date of birth as Jan 10, 1996 and main interests as cinema and music.

Specialist Russian website Kavkaski Uzel (Caucasian Knot) said that Istanbul had become a popular refuge for radically-minded Muslims from the Caucasus who were now fearing a crackdown on their presence.