South Korean President Park Geun Hye and US Vice President Joe Biden agreed Friday that the two countries will work closely together over a regional row surrounding China's unilateral expansion of its air defense zone, Seoul's Yonhap News Agency reported. The air zone row, which has dramatically escalated tensions in Northeast Asia, was a key topic when Park held talks with Biden, as has been with the top American official's earlier stops in Japan and China, the report said. When Park outlined South Korea's position on the issue, Biden "appreciated President Park's explanation and South Korea's efforts," Seoul's Foreign Minister Yun Byung-se was quoted as telling reporters, declining to be more specific on the US position. "The two sides agreed to continue close consultations on this issue," he said. The Chinese zone above the East China Sea overlaps those of South Korea and Japan, and includes the South Korean-controlled reef of Ieodo as well as some small islands. Beijing on November 23 demanded all aircraft entering the zone to notify Chinese authorities beforehand. In a show of defiance, South Korea has flown aircraft through the zone, as has the US and Japan. Seoul has also been preparing to expand its own air zone after Beijing refused to reconsider its decision when the sides held high-level defense talks last week. At the start of the meeting, Biden said US commitment to Asia should never be questioned. "I want to make one thing absolutely clear. President Barack Obama's decision to rebalance to the Pacific basin is not in question," Biden said at the start of the meeting, referring to Obama's "pivot to Asia" policy. "The United States has never been a good bet to bet against America. America will continue to place its bet on South Korea," he said. The US has said it won't recognize the Chinese zone. Last week, the US military flew a pair of B-52 bombers through the zone without notifying Beijing, raising fears of a clash between the two superpowers. But Washington's position appeared to have softened since. The US Federal Aviation Administration later told American airlines to comply with protocol of submitting flight plans before entering foreign air defense zones, though US officials claimed that it doesn't indicate recognition of China's zone but adherence to existing protocol to ensure civilian passenger safety. In Tokyo, Biden said the US is "deeply concerned" about China's move, but stopped short of openly demanding China retract its decision. His talks with Chinese President Xi Jingping produced little progress, though Biden said he was "very direct about our firm position and our expectations in my conversations with President Xi."