China's new air defense identification zone over the East China Sea has caused "significant" unease in the region, Vice President Joe Biden said on Thursday, adding he had stated Washington's firm objection to the move during talks in Beijing. Biden had around five hours of discussions with President Xi Jinping on Wednesday, with both leaders laying out their perspective on an issue that has rattled East Asia. The zone, two thirds the size of Britain, covers an area that includes islands at the heart of a territorial dispute with Japan.