Taiwan has been striving to free two senior intelligence agents kidnapped by China and held for seven years, the island's spy chief confirmed Wednesday.

Chu Kung-hsun and Hsu Kuo-chang, both colonels in the Military Intelligence Bureau, were kidnapped in Vietnam and taken to China in 2006.

Taiwan said Monday its military planes have made about 30 flights into a part of China's newly declared air defense zone which overlaps a similar Taiwanese zone.

China's unilateral announcement on November 23 of an Air Defense Identification Zone (ADIZ) in the East China Sea has angered the United States, Japan and South Korea as well as Taiwan.

Taiwan said Monday it had terminated diplomatic relations with Gambia, after the West African nation's move to cut ties shocked Taipei and left it with a dwindling number of foreign allies.

Gambian President Yahya Jammeh caught Taiwan unawares Thursday when he said his government had broken off diplomatic ties after 18 years owing to "strategic national interest.”

Taiwan has sent senior diplomats to Gambia in a last-ditch effort to restore diplomatic relations after they were unilaterally broken off by the West African nation, officials said Sunday.

Foreign ministry spokeswoman Anna Kao said officials including Richard Shih, the island's ambassador to Gambia from 2008 through 2011, had arrived in Banjul.

Taiwan on Friday expressed shock and regret over Gambia's surprise announcement that it had broken off ties with the island after 18 years in its "strategic national interest".

"Our government express shock and regret that Gambian President Yahya Jammeh sent a letter to our embassy in Gambia on November 14 to inform us the immediate termination of ties," vice foreign minister Simon Ko told a news conference in Taipei.

Researchers in Taiwan on Thursday called on watchdogs to keep up their guard after a flu virus that commonly circulates among chickens was found for the first time in a human being.

The strain found in a 20-year-old patient from central Taiwan was of relatively low virulence, but the risk is that it could mix with other viruses to become more dangerous, they said.

Taiwan signed a free trade deal with Singapore on Thursday, its first with a Southeast Asian country, as the diplomatically isolated island steps up efforts to join regional economic blocs.

The "economic partnership agreement" was signed in Singapore just months after Taiwan struck a similar deal with New Zealand, its first with a country that has diplomatic ties with China.

A strong earthquake struck eastern Taiwan Thursday, shaking buildings in the capital and across much of the island and sending panicky residents running for shelter.

But initial reports suggested the island escaped with few injuries and little damage.

Taiwan Thursday displayed its first long-range submarine-hunting aircraft, days after Beijing showed off its nuclear-powered submarine fleet in yet another sign of China's fast expanding military might.

Taiwan's military introduced the Lockheed P-3C Orion at a ceremony presided over by President Ma Ying-jeou at an airbase in the southern county of Pingtung.

Two crew members and a weather station employee were killed Wednesday when a helicopter crashed into a mountain in central Taiwan, officials said.

The Sunrise Airlines helicopter was carrying supplies to a weather station on Yushan, the island's highest mountain, when it crashed into the mountain's north peak, the National Fire Agency said.