By Pavel Polityuk and Olesya Astakhova KIEV/KRASNOYARSK, Russia (Reuters) - Ukraine has sent a small prepayment of $15 million to Russia for March natural gas deliveries, energy officials from the two sides said on Friday, after Moscow threatened to cut off supply. In their latest dispute, Ukraine and Russia have argued over who should pay for Russian gas sent to two rebel-held areas of eastern Ukraine after supply from Kiev was cut off. Moscow has also warned that Ukraine needs to prepay for future deliveries as a temporary deal for winter gas brokered by the European Commission ends next month.

Prime Minister David Cameron vowed to defeat jihadists and defended Britain's secret services on Friday after media reports named Islamic State executioner "Jihadi John" as London graduate Mohammed Emwazi. "We will do everything we can with the police, the security services, with all that we have at our disposal, to find these people and put them out of action," Cameron said at a press conference in Wales. "Jihadi John", believed to be responsible for beheading at least five Western hostages, was identified Thursday by media and experts as a Kuwaiti-born computing graduate who had lived in London since the age of six.

Senior officials from Iran and six powers negotiating with Tehran over its nuclear program will hold more talks in Montreux, Switzerland on March 5, the European Union said on Friday. The talks between political directors will be preceded by a series of bilateral meetings, EU spokeswoman Catherine Ray told reporters. The State Department announced on Thursday that U.S. Secretary of State John Kerry would meet with Iranian nuclear negotiators in Montreux next week.