A top North Korean military official renewed Pyongyang's threats of war against South Korea and its allies on Wednesday, even as China warned against further provocation on the tense peninsula.

In a speech to mark North Korea's “Army Day,” Vice Marshal Ri Yong-ho said his country is armed with weapons that are capable of destroying the U.S. military “in a single blow.” He also vowed to “cut the throats” of anyone who defames Pyongyang's leadership.

North Korea has stepped up its militant rhetoric against Seoul after South Korean President Lee Myung-bak criticized the North for spending money on its failed rocket launch earlier this month instead of feeding its starving population.

Many observers fear that the North may carry out its third nuclear test in an attempt to divert attention from the failed rocket launch. It previously conducted nuclear tests after rocket launches in 2006 and 2009.

But the South's Unification Ministry said Wednesday it has detected no unusual military movement from its neighbor. Spokeswoman Park Soo-jin said there is no indication North Korea has carried out a nuclear test.

“There are various reports regarding a nuclear experiment (in North Korea). We are keeping our eye on them, but there is nothing special detected so far. But we are paying close attention.”

South Korean authorities went on high alert this week after North Korea threatened to carry out “special military action” with “unprecedented means and methods.”

Demonstrators have marched in each country to denounce each other's government. Protesters in Seoul burned North Korean flags and chanted anti-Pyongyang slogans Wednesday, while North Koreans recently destroyed effigies of the South's President Lee.

Chinese Vice Foreign Minister Cui Tiankai appeared to issue a veiled warning Wednesday to Beijing's neighbor and ally North Korea not to carry out any acts that would escalate tensions in the region.

“China will oppose anything that might jeopardize peace and stability on the Korean peninsula and in Northeast Asia, as this would damage China's national security interests and in the interest of the relevant parties, as well.”

Earlier this month, China joined the 14 other members of the U.N. Security Council in issuing a condemnation of the North's failed rocket launch.

North Korea rejected international complaints that its launch was actually a disguised missile test, conducted in violation of U.N. resolutions. Pyongyang claims the launch was aimed at placing a weather satellite into orbit.