A top military official on Monday confirmed for the first time in public that China is building an aircraft carrier.

"I have nothing more to say about Chinese aircraft carriers, since prominent media outlets have already reported on them so much," said Chen Bingde, chief of the People's Liberation Army (PLA) General Staff. "Our American friends all know that China bought an old aircraft carrier, the Varyag, from Ukraine. It's very valuable for us to research these things this way."

China is the last permanent member of the United Nations Security Council to get an aircraft carrier. Before acquiring Varyag, the country had bought three decommissioned aircraft carriers for the purpose of studying them. Two of them, the former Russian carriers Minsk and Kiev, have been turned into theme parks.

Liu Huaqing, former vice-chairman of China's Central Military Commission, who died in January, first conducted studies in 1970 on the feasibility of building a domestic aircraft carrier. Not until decades later, though, did China start to refit the Varyag and consider building a carrier.

"China is a big country and we have quite a large number of ships, but they are only small ships," Chen said. "This is not commensurate with the status of a country like China."

Having 11 aircraft carriers makes the United States "a real world power", he said.

Much of China's military technology is similar to what the US was using from 20 years to 30 years ago, Chen said.

Mike Mullen, chairman of the US Joint Chiefs of Staff, who is on a visit to China, said while "great symbolism" is associated with China's first aircraft carrier, "sometimes matching the actual capability versus the symbolism, there can be a gap there".

Hong Yuan, chief of the Center for Arms Control and Nonproliferation Studies at the Chinese Academy of Social Sciences, previously said there will be "a prolonged process" before the Varyag can be even remotely effective.

The 67,500-ton Varyag is considerably smaller than the Japan-based US carrier George Washington, which has a displacement of more than 100,000 tons. But when it goes into service, it will make China one of four countries besides the US, France and Russia to have an operational carrier with a displacement of 50,000 tons or more.

The Varyag was bought from Ukraine for $20 million in 1998. According to reports, it has been undergoing refitting work at a shipyard in the northeastern coastal city of Dalian since 2005.

"This has been a gigantic project and is virtually as complicated as building a brand-new aircraft carrier," an unidentified source with the military industry in Dalian was quoted as saying by the Kanwa Asian Defense magazine.

Just as the news came out that the Varyag will begin initial sea trials probably either late this month, in early August or later in the year, rumors arose saying that another aircraft carrier is being built in Shanghai.

In earlier June, the Hong Kong Commercial Daily quoted Chen as saying - during his flight to the US - that the construction of at least one aircraft carrier is "under way, and not finished yet".

Chen did not disclose on Monday how many aircraft carriers China plans to build.

He did acknowledge, though, that Beijing is developing the Dongfeng-21D, a ballistic missile with a maximum range of 2,700 kilometers and the ability to strike moving targets - including aircraft carriers - at sea.

"The missile is still undergoing experimental testing and will be used as a defensive weapon when it is successfully developed, not an offensive one," Chen said.

"It is a high-tech weapon and we face many difficulties in getting funding, advanced technologies and high-quality personnel, which are all underlying reasons why it is hard to develop this," he added.

The steam-powered Varyag is expected to serve primarily as a training vessel for pilots and deck crews. Speculation over what is going to be stationed on it has become more rampant in recent times. According to online leaks, the vehicles it carries may include the J-15 fighter, the JT-9 naval trainer and the Z-8 helicopter.

It is uncertain when the Varyag will be made operational and where it will be based.