The request came as Washington demanded what sources said are exorbitant prices on a range of arms that Taiwan seeks to purchase -- from U.S.-made missiles to helicopters -- and dithers over the island's longstanding request to kick-start the procurement process for F-16 fighter jets.

Amid the "price-gouging," the U.S. military -- without prior consultation with Taiwan -- recently asked the island to pay for the addition of costly "anti-tampering" technology in an US$800 million early-warning radar system, the official said, speaking on condition of anonymity.

"The Taiwanese military is really frustrated with the U.S. (over radar issues)," the official told Kyodo News, adding that the price tag for the unscheduled security measures was nearly NT$2 billion (US$61 million).

"Implementing security measures is standard. But why has the U.S. sprung this on Taiwan some three years after the project started and as it's nearing completion?" the official said.

For Taipei, the last-minute request points to Washington's apparent concern over the security of U.S.-made military platforms on the island amid warming relations across the Taiwan Strait, the official said.

"The U.S. is worried about its Taiwan-based technology becoming compromised as cross-strait ties warm...and the island becomes more vulnerable to Chinese espionage," the official said.

Asked for comment, a media liaison officer in Taiwan's Defense Ministry confirmed the extra security costs, saying the ministry was "looking into the matter." The official declined further comment and requested anonymity.

In 2006, Washington hired U.S. defense contractor Raytheon to build the radar facility, reportedly on Leshan Mountain in central Taiwan. Scheduled to begin operations this year, the radar's capabilities include detecting and tracking incoming missiles from China, according to a recent report by the U.S. Congressional Research Service.

But mudslide-induced delays have abounded, according to Defense News, a U.S. newsweekly covering military affairs. Indeed, a recent job advertisement on Raytheon's website seeks an engineer to supervise "the surveillance radar program at the Taiwan field site...and work in a remote and hazardous environment."

Since construction began, Washington has "on many occasions requested more funds" from Taipei beyond the radar's sticker price, citing washouts of mountain roads and loose soil, Taiwan's China Times, a vernacular daily, reported last week.

But Washington's latest radar-related request fits with a more recent pattern of overcharging Taipei -- often for political or security- related reasons -- the official said, citing separate deals over U.S.- made missiles and helicopters.

Taiwan's latest bid to procure U.S.-made Javelin antitank missiles and launchers hit a brick wall after Washington raised the price of each missile from US$80,000 to US$240,000 without explanation, the official said.

Washington also recently added more than US$20 million to a deal for three U.S.-made search-and-rescue helicopters for Taiwan's air force -- again, without explanation -- the China Times reported.

"These American contractors...treat us like their sugar daddy," said ruling Nationalist Party (KMT) lawmaker Lin Yu-fang, according to the daily.

But while the United States allegedly seeks to overcharge Taiwan, or -- in the case of the radar -- unexpectedly requests extra fees, Washington has gone silent on Taipei's requests for other platforms, especially F-16 fighter jets.

Taipei has requested 66 F-16C/Ds since at least 2007, but Washington has declined to initiate the deal because of Chinese pressure, a Western diplomat said, adding, "For Beijing, F-16s are the red line."

Communist-ruled China has claimed to Taiwan ever since 1949 when the Nationalists fled to the island after losing a bloody civil war on the mainland. Beijing has vowed to attack the self-ruled island should it formalize its de facto sovereignty, while Washington serves as Taipei's security benefactor.

Despite their own flourishing economic ties, Washington and Beijing remain strategic rivals, with the former concerned over the latter's alleged espionage activities in Taipei and the possibility, however remote, that a Chinese takeover of the island would see a host of U.S. arms fall into Chinese hands.

Since Taiwanese President Ma Ying-jeou took office last year, cross- strait tensions have eased considerably, with Ma forging or strengthening a bevy of bilateral trade and logistical links through high-level talks.

Still, even amid warming cross-strait relations, China continues to deploy some 1,300 ballistic and cruise missiles against Taiwan, according to the island's military -- a threat necessitating the Raytheon-built radar.

However, although Washington apparently welcomes the cross-strait thaw, the new closeness between Beijing and Taipei bodes ill for sophisticated U.S. weaponry already on, or sought by, the island.