Samantha Lewthwaite, 30, was gunned down by a Russian sniper two weeks ago, alleged Regnum news agency in Moscow.
One of Britain’s most wanted people, she was reported last month as fighting for the Islamic State’s terrorists in Syria.
The extraordinary Russian claim could not be verified last night.
Lewthwaite was married to 7/7 suicide bomber Germaine Lindsay, 19, a Jamaican-born Yorkshireman, and allegedly left Britain in 2009 before being linked to atrocities in Africa.
‘One of the world’s most wanted terrorists Samantha Lewthwaite who fought as part of a Ukrainian battalion has been killed by a volunteer sniper,’ said the news agency report.
‘According to our information, the White Widow fought on the side of Ukrainian volunteer battalion Aidar as a sniper.
She was killed by ‘a volunteer sniper who came to fight at the Lugansk front from Russia’.
The report continued: ‘The Russian sniper who killed the British terrorist now has a price of nearly one million dollars on his head from Ukrainian special services.’
The extraordinary unconfirmed claim came amid a welter of propaganda from Moscow and Kiev over the Ukrainian crisis.
The claim that Lewthwaite is dead could be an attempt by Russia to bolster its anti-terrorism credentials at a time when it is controversially massing armour and troops in Ukraine.
Nato today warned that Russian military equipment is entering Ukraine on a large-scale.
‘Across the last two days we have seen the same thing that OSCE is reporting. We have seen columns of Russian equipment, primarily Russian tanks, Russian artillery, Russian air defence systems and Russian combat troops entering into Ukraine,’ said US General Philip Breedlove, supreme allied commander.
The Organisation for Security and Cooperation in Europe (OSCE) said: ‘The level of violence in eastern Ukraine and the risk of further escalation remain high and are rising,’ said Michael Bociurkiw of the OSCE’s Special Monitoring Mission.
In response, Ukraine has said that it’s preparing for all-out war.
Ukrainian Defence Minister Stepan Poltorak told a cabinet meeting: ‘The main task I see is to prepare for combat operations. We are doing this, we are readying our reserves.’
Reports last month claimed Lewthwaite – a former soldier’s daughter – joined Islamic State earlier this year and became one of the most powerful women in the network.
Born in Northern Ireland and schooled in Aylesbury, she was not previously linked to Ukraine.
She was responsible for training a special team of female suicide bombers in Syria, it was alleged.
Lewthwaite allegedly trained and mentored British converts who volunteered to fight for the IS.
The 7/7 attack on the London transport network on 7 July 2005 killed 52 people.
Lewthwaite had been viewed as the innocent Home Counties’ wife of a suicide bomber but was later seen as ‘the world’s most dangerous female terrorist’.
In June 2012 two men and a white woman – believed to be her – wearing Islamic dress killed three and injured 25 at a beer garden in Mombasa after throwing grenades at foreigners watching England play Italy at Euro 2012.
She was also linked to another grenade attack which killed security guards in an upmarket restaurant.