Japan is ready to open a contested tract of the East China Sea to fishing boats from Taiwan, officials in Taipei say, a rare concession in a bitter territorial dispute that involves heavyweight China and has the United States on guard.

Tokyo is “willing to extend the fishing area” to Taiwanese boats, though the boundaries have yet to be worked out, Taiwan’s Foreign Minister David Lin told reporters on Wednesday.

Taiwan has sought such a deal since 1996 as it vies with Japan and China for control of eight uninhabited islets that anchor a massive, strategic swathe of the sea rich in fish and believed to hold reserves of oil and natural gas. If the deal goes through it could mean that Japan – which has not conceded any territory since the end of World War II – wants Taiwan on its side in the struggle against China over the disputed ocean.

Japan controls the islets and would make the fishing area concession to Taiwan, not China, though Beijing has put pressure on Japan with airplanes, boycotts, and mass street protests.

“Without conceding anything on history or territory, Japan’s showing Taiwan a little leg on fishing to play it off the mainland [China], and to maintain its reasonably good relations with Taiwan,” says Sean King, senior vice president with the political consulting firm Park Strategies in New York.

Japan, the world’s No. 3 economy, wants better relations with No. 2 China but is locked in the islet dispute and a list of others stemming from the World War II era. In a showdown in January over the islets that Tokyo calls the Senkaku and China calls the Diaoyu, Japan raised its defense budget as China sent military planes.

US officials, who rely on East China Sea shipping lanes, have urged calm.

Taiwan opposes Tokyo’s claim to the East China Sea islets but sees Japan as an informal ally along with the US in keeping Beijing in check militarily.

Conservative Japanese lawmakers and local officials regularly visit Taiwan, particularly when their country’s relations with China become strained.

“Taiwan is important to Japan both as a neighbor and an economic partner, and what’s important to Taiwan is to retain a unique relationship with Japan,” says Raymond Wu, managing director of the e-telligence risk consultancy in Taipei.

China will keep quiet on the Taiwan-Japan deal in the works as not to upset Taiwan, which it hopes will side with Beijing in the sea dispute, Mr. King says.

But China claims sovereignty over self-ruled Taiwan itself and bristles, if only in private, when it makes deals with other governments, especially when those agreements threaten Beijing’s interests.

After 16 rounds, Japan cut off fishing rights talks with Taiwan in 2009 over the sovereignty issue. The two governments have overlapping claims to waters near the islets, and the Japanese coast guard would periodically chase off Taiwanese boats.

Taiwanese fishing boats traditionally trawl in waters near the disputed islets, which are 222 km (138 miles) from home.

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The two sides met in mid-March to plan another round of talks. Taiwan wants clear boundaries for an expanded fishing area, the foreign minister said. A detailed deal would lift the image of Taiwan President Ma Ying-jeou, who has been seen as weak on foreign policy since taking office in 2008.

“The two sides have an agreement in principle,” Mr. Lin said. “But where are the boundaries of the expanded area? That’s the key to our talks now.”