* North Korea carries out third nuclear test
* Blast slightly larger than two previous tests (Adds quote, second Russian estimate on blast size)
MOSCOW, Feb 12 (Reuters) - Russia's Defence Ministry said the power of North Korea's nuclear test blast on Tuesday surpassed seven kilotons, a ministry source told the Interfax-AVN military news agency.
South Korea said earlier on Tuesday that the size of the seismic activity indicated a nuclear explosion slightly larger than the North's two previous tests at six to seven kilotons. The Hiroshima bomb was, by comparison, around 20 kilotons.
The Russian Defence Ministry source told Interfax-AVN that specialists were still trying to determine the exact magnitude of the explosion but that it was "more than" seven kilotons.
Another Russian news agency, RIA, later quoted a source in a nuclear arms control watchdog as saying the power of the blast was estimated at around five kilotons. There was no immediate explanation for the difference in the estimates.
North Korea confirmed it had carried out the nuclear test and said it had used a miniaturised device that had a greater explosive force than previous nuclear tests, carried out in 2006 and 2009. (Reporting by Alissa de Carbonnel; Editing by Timothy Heritage)