U.S. Vice President JD Vance makes an opening statement at the start of a quadrilateral meeting between the U.S., Iran, Pakistan, and Qatar at the Lake Lucerne Summit, aimed at advancing a deal to end the Middle East conflict, at Buergenstock Resort Lake Lucerne, near Stansstad, Switzerland, June 21. Reuters-Yonhap

OBBUERGEN, Switzerland — High-level U.S.-Iran talks on their interim deal to end the war had a tense start Sunday in Switzerland as Tehran took offense at comments by President Donald Trump, who threatened to attack and told Iran's president to watch what he says.

The comments from afar — on social media and to news outlets — complicated efforts by Vice President JD Vance and mediators Pakistan and Qatar to keep Iran engaged in discussions meant to address thorny issues like Tehran's nuclear program, the Strait of Hormuz and the unfreezing of billions of dollars in Iranian assets.

Before anything, however, Iran wants to discuss Lebanon, where Israel's military has been fighting the Iranian-backed Hezbollah militant group, since the deal halts conflict on all fronts.

“Iran must immediately stop their highly paid PROXIES in Lebanon from causing trouble,” Trump said on social media. “If they don’t, we’ll hit Iran very hard again, just like we did last week, only harder!!!”