SEOUL, South Korea (AP) – North Korea said Wednesday it would respond with “physical” measures to counter U.S. pressure against the communist regime after it claimed to conduct a successful nuclear test.

“If the U.S. increases pressure upon the (North), persistently doing harm to it, it will continue to take physical countermeasures, considering it as a declaration of a war,” the North’s Foreign Ministry said in an English-language statement carried by the official Korean Central News Agency. The North didn’t specify what the measures would be.

North Korea “was compelled to substantially prove its possession of nukes to protect its sovereignty and right to existence from the daily increasing danger of war from the U.S.,” the North said, criticizing an alleged nuclear threat from Washington and sanctions.

The North “is ready for both dialogue and confrontation,” the ministry said. The statement was the first official announcement from the North Korean government since KCNA reported of the Monday test.

The ministry said the North “successfully conducted an underground nuclear test under secure conditions,” echoing the earlier report.

Despite the test, the North said “it still remains unchanged in its will to denuclearize the peninsula through dialogue and negotiations.”

Pyongyang claimed the test didn’t violate a September 2005 agreement reached at international arms talks where the country pledged to abandon its nuclear program in exchange for aid and security guarantees.

“On the contrary, it constitutes a positive measure for its implementation,” the North said, without elaborating. The North also criticized the moves at the U.N. Security Council to adopt sanctions against the regime in the wake of the claimed test.