The air force is currently planning midlife upgrades for its roughly 150 F-16A/B models, which it purchased from the United States in 1992, and its some 130 Indigenous Defense Fighters, which were developed and manufactured locally in the 1990s.

The upgrades are aimed at boosting the fighters' performance and avoid a "gap in Taiwan's war-fighting capabilities," the island's semi- official Central News Agency reported Friday.

The upgrades would seek to address "the trend of the tipping of the military balance in the Taiwan Strait," the air force reportedly said, without elaborating.

On Thursday Defense Minister Kao Hua-chu told lawmakers that the military was considering mothballing the some 60 French-made Mirage models that Taiwan bought from France from 1997-1998. Factors including Chinese pressure on France and Paris' decision to halt the production of the Mirage in 2007 have contributed to a chronic lack of spare parts and logistical support for Taiwan's fleet, according to local media.

Besides Taiwan's struggle to maintain its Mirages, the island is struggling to replace its other aging fighters as the United States, Taipei's security benefactor, increasingly shies away from providing big-ticket weapons systems.

Since 2007, Taipei has appealed to Washington to kick-start the procurement process for 66 more advanced F-16 fighter jets, but Washington has been reluctant to sell them for fear of irking Beijing, which claims the self-ruled island as its own.

For its part, Taiwan has hesitated to upgrade its IDFs amid uncertainty over whether the United States will sell it the 66 F-16C/D fighters.

In the meantime, China's military has grown exponentially, with "the balance of military power in the Taiwan Strait now clearly tipped in China's favor," a recent Taiwan Defense Ministry report states.

At a conference in Taipei last week, Michael Green, former senior director for Asian affairs at the White House's National Security Council, said Washington's dithering on the F-16 jets throws into doubt its security commitments to Taipei.

"These decisions (on arms sales)...could have...strategic consequences if the F-16C/D sales do move forward in 2010," Green, now chairman of Japan research at the U.S.-based Center for Strategic and International Studies, said, warning that the gap in capability between the air forces of Taiwan and China is rapidly growing.