The United States has an "obligation" to fill its backlog of arms sales to Taiwan and there is a bipartisan effort to ensure this happens, a U.S. lawmaker said on Friday, as the island's defence ministry pushed for solutions from Washington. Taiwan has since last year complained of delays to U.S. weapon deliveries, such as Stinger anti-aircraft missiles, as manufacturers turned supplies to Ukraine as it battles invading Russian forces. The issue has concerned some U.S. lawmakers and officials too. The United States, like most countries, has no formal relations with Taiwan - which China claims as its own -...