U.S. Democratic presidential candidate Barack Obama Wednesday called for active diplomacy to check nuclear proliferation, saying the Bush administration's lack of diplomacy resulted in North Korea developing eight nuclear warheads.

In an interview with a CBS program, Obama, however, did not elaborate on where he had obtained the information on the North's possession of eight nuclear weapons.

"North Korea, when we weren't talking, developed eight nuclear weapons," Yonhap News quoted Obama as saying. "And when we started talking, we've now arrived at a possibility where we could get those nuclear weapons and those systems dismantled."

The Illinois senator was talking about the recent developments in the six-party talks on ending North Korea's nuclear ambitions.

The intelligence community estimates the number of North Korea's nuclear warheads at five to 10, based on the up to 50 kilograms of weapons-grade plutonium the North is believed to have produced over the past decade or so at its nuclear reactor in Yongbyon, north of Pyongyang.

The Bush administration had refused to deal directly with Pyongyang and Tehran for the past years unless they drop their nuclear ambitions. But in recent months it has actively engaged North Korea, persuading it to present its nuclear program list, blast a nuclear cooling tower and agree to disable its nuclear facilities by the end of October in return for energy aid.

Washington is in the midst of a 45-day process running to Aug. 11 to delist the North as a state sponsor of terrorism, and the Bush administration has already removed some sanctions.

"You know, engaging in tough diplomacy is not a sign of weakness, it's a sign of strength," Obama was quoted as saying.

Obama defended Israel's controversial recent bombing of a suspected nuclear facility in Syria. "I think that there was sufficient evidence that they were developing a site," and were "using a blueprint that was similar to the North Korean model," he said. "There was some concern as to what the rationale for that site would be."