China expressed its opposition Thursday to unilateral sanctions against North Korea saying they could raise tension, after the United States imposed new curbs on the isolated country in retaliation for its nuclear and rocket tests. U.S. President Barack Obama on Wednesday imposed sweeping new sanctions on North Korea intended to further isolate its leadership after recent actions seen by the United States and its allies as provocative.

The new sanctions threaten to ban from the global financial system anyone who does business with broad swaths of North Korea's economy, including its financial, mining and transport sectors. The so-called secondary sanctions will compel banks to freeze the assets of anyone who breaks the blockade, potentially squeezing out North Korea's business ties, including those with China.

Asked whether China was worried the sanctions could affect "normal" business links between Chinese banks and North Korea, Foreign Ministry spokesman Lu Kang said this was something China was "paying attention to".

"First, as I've said many times before, China always opposes any country imposing unilateral sanctions," Lu told a daily news briefing in Beijing. "Second, under the present situation where the situation on the Korean Peninsula is complex and sensitive, we oppose any moves that may further worsen tensions there. Third, we have clearly stressed many times in meetings with the relevant county, any so-called unilateral sanctions imposed by any country should neither affect nor harm China's reasonable interests."

China is North Korea's sole major ally but it disapproves of its nuclear program and calls for the Korean peninsula to be free of nuclear weapons.

While China has signed up for tough new U.N. sanctions against North Korea, it has said repeatedly sanctions are not the answer and that only a resumption of talks can resolve the dispute over North Korea's weapons program.

The U.S. measures, which vastly expand a U.S. blockade of North Korea, prohibit the export of goods from the United States to North Korea.

U.S. officials previously believed a blanket trade ban would be ineffective without a stronger commitment from China, North Korea's largest trading partner.

North Korea conducted a nuclear test on Jan. 6, and on Feb. 7, it launched a rocket that the United States and its allies said employed banned ballistic missile technology. China signed on to the new U.N. sanctions against North Korea this month.

But U.S. officials and experts have often questioned China's commitment to enforcing sanctions on North Korea. China fears that too-harsh measures will destabilize the North.