WASHINGTON - North Korea may be preparing for its third nuclear test, a show of defiance as the United Nations considers new sanctions on the country for conducting a nuclear test in May, according to a U.S. official.

North Korea conducted an underground explosion May 25, its first since a 2006 test. The official, who spoke yesterday on condition of anonymity, would not provide details regarding the assessment.

A draft U.N. resolution proposed Wednesday would impose tough sanctions on North Korea's weapons exports and financial dealings and allow inspections of suspect cargo in ports and on the high seas. North Korea has threatened to retaliate.

North Korea already is a pariah to many countries and has been under tough economic sanctions for years. Last month's reported test defied a Security Council resolution adopted after the North's first underground atomic blast in October 2006.

The White House National Security Council would not comment on the assessment of a possible third test.

"We have come to expect North Korea to act recklessly and dangerously," NSC spokesman Mike Hammer said. "But while the world unites to pass a strong new Security Council resolution, it is clear that North Korea's behavior is succeeding only in further isolating itself."

President Obama's special envoy on North Korea, Stephen Bosworth, said yesterday that the United States was determined to make sure the North faced serious consequences for its actions. Bosworth told lawmakers at a hearing that the administration was considering freezing North Korean accounts at banks outside the country.

Tensions rose further yesterday when North Korea demanded a 3,000 percent increase in rent for a lucrative joint industrial park. The complex has been the biggest symbol of reconciliation between North and South Korea.

Pyongyang also seeks a fourfold increase in wages for 40,000 workers employed by South Korean companies at the park, in the North Korean border town of Kaesong. The demands were made during talks between the two sides at Kaesong, an official said.

The complex, which opened in 2004, combines South Korean capital and technology with cheap North Korean labor.