China has lashed out at the United States in response to a Pentagon report expressing continued concern over China's rapid military buildup and the rising Chinese threat to Taiwan. But the Chinese government admits to boosting its forces, both for defense and what it calls "national reunification" purposes.

China routinely rejects the Pentagon's annual reports to Congress and this year was no exception. Foreign Ministry spokesman Liu Jianchao - at a regular briefing - called the 2006 report and the concerns expressed in it "groundless."

U.S. officials have called for China to be more transparent in disclosing the details of its military buildup and the reasons for it. Liu said China rejects the calls.

"Some people criticize China's military spending as not transparent. China cannot accept that," Liu said. "We have already announced to the whole world, clearly and publicly, our legally formulated national defense budget."

Beijing's communist leadership this year announced plans to boost defense spending by 14.7 percent to about $35 billion. The Pentagon and some military analysts outside China say that figure is probably three times higher.

In their report this week, U.S. defense officials say they have been surprised by the pace and scope of China's military expansion. They say Beijing's drive to purchase more advanced weapons systems, aircraft, and ships indicate that China is looking to project its military power beyond its neighbors and its traditional rival, Taiwan.

But Taiwan remains a major military focus. The mainland's communist government considers the democratically ruled island a part of its territory and has vowed to take it by force if it declares formal independence.

In their report this week, U.S. officials said China has increased the number of missiles capable of reaching the island.

Liu said his country is modernizing its military for defensive purposes. But he also mentioned reunification as a reason for the buildup.

"We are facing the important tasks of safeguarding the country's sovereignty, territorial integrity, and national reunification," Liu explained. "So, China will properly increase military expenditures and push forward our national defense modernization. This is completely normal."

Chinese officials announced a new military technology program to develop its own advanced weaponry during the next 15 years. Until now, China has relied primarily on systems purchased from abroad.