(Adds quotes, IAEA comment)
VIENNA, Feb 12 (Reuters) - The magnitude of an unusual seismic event that North Korea said was a nuclear test measured 4.9 on the Richter scale, a monitoring agency said on Tuesday, bigger than the 4.52 measured when the North carried out a test in 2009.
The Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO) also estimated the time for the event as around 0258 GMT.
"On the seismic signal picked up by our monitoring system in North Korea this morning: time: 2.57.51 GMT, magnitude: 4.9 on the Richter scale," the CTBTO said on Twitter.
Tibor Toth, CTBTO executive secretary, said in a statement he was "gravely concerned by this action, which deserves universal condemnation."
Toth added: "Nuclear testing needs to end once and for all."
The U.N. nuclear watchdog, like the CTBTO based in Vienna, expressed "deep regret" about the North's announcement it had carried out a third nuclear test since 2006.
"This is ...in clear violation of U.N. Security Council resolutions," Yukiya Amano, Director General of the International Atomic Energy Agency (IAEA), said in a statement.
(Reporting by Fredrik Dahl; Editing by John Stonestreet)