Taiwan's president, Ma Ying-jeou, yesterday rejected the mainland's request to open up the no-fly zone along the centre line of the Taiwan Strait for civilian flights. Political analysts said Beijing's bold request - which seemed unreasonable to most Taiwanese politicians - was aimed at testing how far the island's leader was prepared to go in cross-strait ties. In a meeting with a Taiwanese economic observer group on Thursday, Wang Yi, director of the Taiwan Affairs Office of the State Council, told delegation head Lai Shyh-bao that Beijing hoped the number of direct cross-strait flights would be sharply increased by opening up the centre of the Taiwan Strait. But the request sparked an outcry in Taiwan's political and military circles, and Mr Ma, who is in Panama, turned down the request yesterday, citing security concerns. '[We] told the mainland very clearly in the past that the centre line of the Taiwan Strait is a key training base for our air force which is impossible to open up,' Mr Ma said at a press conference in Panama City. 'We are not attempting to create trouble [for cross-strait ties], but [the centre line] relates to our security,' he said. The US Army came up with the centre line, or Davis Line, in 1950 to create an identification zone for air defence purposes. It aims at preventing cross-strait military conflicts. Neither the mainland nor Taiwan's Kuomintang recognised the line as it violated the 'one-China policy', until former Taiwanese president Lee Teng-hui issued his 'two states theory' in 1999. Taipei-based political commentator Nan Fangshuo said Beijing had attempted to test how many concessions Mr Ma was willing to make, while also assessing the Taiwanese public's trust of the mainland. He said Mr Ma's swift refusal had shown mutual trust to be shallower than some might have expected. Another Taipei-based political analyst, Paul Lin, said Mr Wang's request also highlighted Beijing's lingering concerns over Mr Ma. 'Or maybe Beijing wanted to help President Ma improve his low public support through a silly request that gives Mr Ma the opportunity to show the Taiwan people he doesn't want to sell the island to Beijing,' Mr Lin said, referring to mounting criticism of Mr Ma for sacrificing Taiwanese interests in his attempts to befriend the mainland. The island's Mainland Affairs Council, Ministry of Defence and Civil Aeronautic Administration all opposed the proposal. 'We are set against the request because the state of hostility across the Taiwan Strait remains,' a Ministry of Defence spokesman said. 'If [the centre line] is opened up, it means Taiwan's air force has no more early warning if war between the two sides breaks out.' Meanwhile, Mr Ma assured Panama's national assembly on Thursday that Taiwan's ties to traditional allies abroad would not be affected by its increasing rapprochement with the mainland.