US President Joe Biden said on Tuesday that China's leader Xi Jinping made a "big mistake" by not attending the Glasgow climate and G20 summits but said he hoped for talks to prevent conflict."The fact that China is trying to assert, understandably, a new role in the world as a world leader -- not showing up, come on," Biden told a news conference in Glasgow."It just is a gigantic issue and they walked away. How do you do that and claim to be able to have any leadership?" Biden said, adding that the same was true for Russian President Vladimir Putin."It's been a big mistake, quite frankly, for China not showing up. The rest of the world looked at China and said 'what value are they providing?'," Biden said.Xi, who leads the world's largest emitter of carbon emissions responsible for climate change, has not travelled outside of China since the beginnings of the Covid-19 pandemic in early 2020.US officials had earlier expected Xi to meet Biden for the first time as president at this weekend's Group of 20 summit in Rome.The two countries, however, instead said they would meet virtually by the end of the year. Biden said no date has been set.Biden said he hoped that their talks would bring more predictability in relations that have been soured by disputes on myriad fronts, including human rights and China's growing assertiveness on Taiwan."I'm going to be clear. This is competition; it does not have to be conflict. There's no reason there needs to be conflict," Biden said."I have also indicated to him -- and I'm not reluctant to say it publicly -- that we expect him to play by the rules of the road."