May 4 (Reuters) - World Liberty Financial, the crypto venture co-founded by U.S. President Donald Trump and his sons, said on Monday it had filed a defamation lawsuit against Hong Kong-based crypto entrepreneur Justin Sun, in the latest escalation of a dispute between the project and one of its most prominent backers. World Liberty posted a copy of its lawsuit on X in which it accused Sun of launching a "public smear campaign" including claims that it said were false.