By Mushtaq Ali and Sayed HassibPESHAWAR, Pakistan/Kabul, April 1 (Reuters) - Afghanistan and Pakistan have opened a new round of talks in China to end the deadliest fighting between two Muslim nations since the Taliban returned to power in 2021, sources said on Wednesday.Beijing has been trying to mediate a negotiated settlement to the conflict, which has claimed heavy losses on both sides, although many more on the Afghanistan side, since Pakistan launched air strikes in late February.