US bars Hong Kong leader from key economic summit amid diplomatic tensions with China

White House decided to exclude Hong Kong's Chief Executive John Lee from major economic summit due to 2020 sanctions.
Hong Kong government asserts US should follow convention and invite city's leader per APEC rules.
Chinese Embassy strongly opposes US decision, which could impact Xi Jinping's attendance.
Move highlights challenge of sanctioning foreign officials while still engaging governments.
Comes amid US diplomatic efforts to restore dialogue with China, though tensions remain over Taiwan.