The US froze accounts allegedly linked to North Korean illicit activities such as currency counterfeiting and drug trafficking.
In Beijing on Wednesday, the American, North Korean and Chinese envoys were discussing the framework for six-party talks.
Russia, South Korea, China, the US and Japan, having put economic, political and security incentives on the table, are calling on Pyongyang to keep a commitment made last year to "abandoning all nuclear weapons and existing nuclear programmes".
Bell described North Korea's stance as "ridiculous" because the US was "not plotting an attack" against it.
According to him, Pyongyang's first nuclear test on October 9 was in line with its "atomic ambitions" and hopes of causing fissures in the US-South Korea military alliance.
The test outraged the world and triggered UN-backed sanctions. Bell also poured water on any hopes that Kim Jong-il's government would collapse soon.
Pyongyang was capable of withstanding great economic pressure, which would ensure the government's continued rule, he said.
Proliferation experts say it was unlikely that North Korea possesses the technology to make nuclear missile warheads. But should North Korea attack its southern rival, Bell promised to "respond quickly [and] decisively".