New Delhi, Oct 6 : US President Joe Biden said he and his Chinese counterpart Xi Jinping have agreed to abide by the "Taiwan agreement", BBC reported. Biden appeared to be referring to Washington's longstanding "one China" policy under which it recognises China rather than Taiwan. However, this agreement also allows Washington to maintain a "robust unofficial" relationship with Taiwan. The announcement comes amid escalating tensions between Taiwan and Beijing. It has sent record numbers of military jets into Taiwan's air defence zone for four consecutive days, which some analysts say could be seen as a warning to Taiwan's president ahead of the island's national day. Taiwan has its own constitution, military, and democratically elected leaders, and considers itself a sovereign state. Beijing, however, views Taiwan as a breakaway province and has not ruled out the possible use of force to achieve unification with the island. The "One China" policy, which Biden and Xi are believed to have referred to, is a key cornerstone of Sino-US relations but is distinct from the One China principle, whereby China insists Taiwan is an inalienable part of one China to be reunified one day, the report said. "I've spoken with (Mr) Xi about Taiwan. We agree ... we'll abide by the Taiwan agreement," said President Biden. "We made it clear that I don't think he should be doing anything other than abiding by the agreement. On Wednesday, Taiwan's defence minister said military tensions with China were at its worst in more than 40 years. Chiu Kuo-cheng added that China would be capable of mounting a "full-scale" invasion of Taiwan by 2025. Analysts have previously warned that Beijing is becoming increasingly concerned that Taiwan's government is moving the island towards a formal declaration of Independence and wants to deter its President Tsai Ing-wen from taking any steps in that direction, the report said. /IANS