North Korea will not rule out a nuclear test as long as Washington is hostile toward Pyongyang, a newspaper linked to the communist nation said Saturday.

There are growing concerns, bolstered by reports of suspicious activity, that Pyongyang may be planning to follow up its recent missile launches with a nuclear test. Pyongyang claims to have nuclear weapons but hasn't performed any known test.

"We can't say for sure that North Korea will not conduct a nuclear test as part of strengthening its self-defense," said Choson Sinbo, a newspaper published in Japan by a pro-North Korean association linked to the Pyongyang regime.

CountryWatch: North Korea

"The full responsibility for this lies with the U.S., which regards any forces that don't agree with or submit to its logic or actions as evil," the paper said, accusing Washington of trying to topple the North's communist regime.

"It is self-evident that we have to take strong countermeasures to protect our country from that threat," the paper said.

China, the communist North's closest ally and key provider of oil, has agreed with South Korea to cooperate to prevent a possible North Korean nuclear test.

China also has reduced "a significant amount" of its oil supplies to Pyongyang since the July 5 missile launches, South Korea's Chosun Ilbo newspaper said.

The report cited unnamed officials at an oil storage terminal near the Chinese border city of Dandong.

North Korea's Foreign Ministry said in a statement that the regime will "pursue all possible countermeasures to protect our sovereignty and dignity," without elaborating what those measures would be.

The statement referred to U.S. financial restrictions imposed against the communist North for alleged counterfeiting and money laundering.

"It is foolish to think that the issue can be solved through sanctions and pressure," the statement said.

Song Min-soon, South Korea's presidential security adviser, said Saturday that a North Korean nuclear test would be "a grave situation of a different level from missile launches and that South Korea and China have agreed to continue cooperation not to let that situation occur."

Song, who returned from a two-day trip to Beijing on Friday, refused to elaborate how the two countries would cooperate.

South Korea, China, Japan, Russia and the United States have tried in six-party talks to persuade the North to abandon its nuclear program.

South Korea's seismic authorities said they detected a tremor in North Korea on Friday, but ruled out an underground nuclear test.

Talks on the North's nuclear program have been stalled since November, when negotiators failed to make headway in implementing the North's agreement to drop its nuclear program in exchange for aid and security guarantees.

"We have more to gain from implementing this agreement, thus we want to take part in the six-party talks more" than the U.S., said the North Korean statement carried by the official Korean Central News Agency on Saturday.

Pyongyang has since refused to attend the six-party talks until Washington stops blacklisting a bank where the North's regime held accounts, a restriction imposed over the alleged counterfeiting and money laundering.