BEIJING (AP) ― China expressed its opposition Monday to a reported deal between the United States and Taiwan to upgrade Taiwan’s existing fleet of F-16 fighter jets, even though the U.S. apparently rejected the island’s bid for a more advanced version of the plane.

Although the Obama administration has yet to issue a formal notification of the F-16 deals, two congressional aides privy to the results of a Capitol Hill briefing on the issue told the Associated Press it nixed the Taiwanese request for 66 relatively advanced F-16 C/Ds, while agreeing to upgrade the island’s existing fleet of F-16 A/Bs.

The fighter jets have been a dominant issue in the uneasy triangular relationship between Taipei, Washington and Beijing throughout the 3 1/2 year presidency of Taiwan’s Ma Ying-jeou. Despite reducing tensions across the 160-kilometer -wide Taiwan Strait to their lowest level since China and Taiwan split amid civil war in 1949, Ma has pressed for the new warplanes, saying Taipei needs them to continue negotiating with Beijing from a position of strength.

That has put the U.S. in a difficult position, forcing it to try to balance its congressionally mandated responsibility to provide Taiwan with weapons to defend itself against a possible Chinese attack with a desire to keep its increasingly important relations with Beijing on an even keel.

China reacts angrily to any foreign military sales to Taiwan, because it regards the democratic island of 23 million people as part of its territory. It temporarily suspended military exchanges with the U.S. last year after the Obama administration notified Congress it was making $6.4 billion in weapons available to Taiwan, including missiles, Black Hawk helicopters, information distribution systems and two Osprey Class Mine Hunting Ships.

Speaking at daily news briefing in Beijing on Monday, Chinese Foreign Ministry spokesman Hong Lei said China’s opposition to American arms sales to Taiwan has been “consistent and clear.”

Without indicating what action China might take because of the F-16 upgrade, Hong said the United States should “refrain from selling arms to Taiwan so as to avoid impairing bilateral relations as well as the peaceful development of cross-strait relations.”

Hong’s comments were relatively muted in comparison to the ferocity of China’s response when last year’s arms package was announced. While China’s powerful military and nationalistic public opinion have called for retaliation ― including against the U.S. companies involved ― Beijing has so far relied on diplomatic channels to register its unhappiness.

State leaders appear unwilling to see a major disruption in ties ahead of a visit to the U.S. by Vice President and expected future leader Xi Jinping before the end of the year. China is also mindful of public opinion in Taiwan, where a threatening response could undue years of efforts aimed at winning over the island’s 23 million people to the cause of better relations and, ultimately, unification between the sides.

In Taipei, Ma’s office said it would not comment on the decision until it is formally announced ― something that U.S. Secretary of State Hillary Rodham Clinton has promised will happen by the end of this month.

On Friday, Republican Sen. John Cornyn of Texas, where the Lockheed Martin plant that would have built the new F-16s is located, said a negative decision on new F-16s would be a slap in the face to strong ally Taiwan.

Howard Berman, the ranking Democrat on the House of Representatives Foreign Affairs Committee, called provision of the A/B upgrade without the newer planes a “half-measure.” He said Taiwan needed more advanced fighter aircraft to defend itself against an increasing Chinese military threat.

A senior U.S. official said Monday the upgrade to the fighter fleet would still mean the administration has sold more weapons to Taiwan since 2009 than the U.S. had in the four previous years.

The official said that, if true, the reports would mean Taiwan gets 145 planes instead of 66, without a loss in quality and at a cheaper price.

The official spoke on condition of anonymity because of the sensitivity of the issue.

There were no immediate details on the package of upgrades the U.S. is providing for the A/Bs. But even if the package includes sophisticated radar, avionics and missile systems, Taiwan’s air force will still lag far behind its Chinese counterpart, which is equipped with state-of-the-art jet fighter aircraft.

A Pentagon report issued last year painted a grim picture of Taiwan’s air defense capabilities, saying that many of the island’s 400 combat aircraft would not be available to help withstand an attack from the mainland.

Wang Kao-cheng, a military expert at Taipei’s Tamkang University, said Taiwan’s air defenses could get some lift from the upgrade, but that the island is still at a profound disadvantage with Beijing in the number of third-generation warplanes it has at its disposal.

“Taiwan has fallen behind in air superiority as of now, not to mention the fact that China is developing the fourth-generation stealth fighters, which could be very powerful,” Wang said. “The upgrade program will not fill the vacuum left over by the absence of the C/Ds.”