China on Tuesday urged President-elect Barack Obama to work with Beijing to improve its occasionally tense military relationship with the United States, calling on the Pentagon to "remove obstacles." Sr. Col. Hu Changming, spokesman for the Ministry of National Defense, said China - with one of the world's fastest-growing armed forces - looked forward to smoother relations with Washington and its military, the world's largest. "At present, when China-US military-to-military relations are faced with difficulties, we call on the US Department of Defense to remove obstacles ... and create favorable conditions for the healthy growth of military relations," Hu said during a news conference held to present a major military policy paper. China remains opposed to US arms sales to Taiwan, and blocking formal independence for self-governing Taiwan remains the military's chief concern, the paper said. China also views separatist movements in Tibet and the far western region of Xinjiang as the biggest threats to the country's national security. "On these matters, we will not compromise," Hu said.