An electronic board showing the Korea Composite Stock Price Index at a dealing room of the Hana Bank headquarters in Seoul on Monday. (Yonhap) South Korean stocks opened lower Monday as uncertainty over US-Iran peace negotiations intensified following US President Donald Trump's continued threats on Tehran.The benchmark Korea Composite Stock Price Index fell 124.2 points, or 1.37 percent, to 8,928.2 in the first 15 minutes of trading.Overnight, the United States and Iran started negotiations in Switzerland, but soon Iran halted talks after Trump threatened strikes on Iran if Hezbollah keeps attacking Israel.Tehran earlier said it will close the Strait of Hormuz over Israel's ongoing military campaign in Lebanon against the Iranian-backed Hezbollah militant group, citing the interim 60-day deal that stops conflict on all fronts.In Seoul, major market heavyweights led the weak opening.Market bellwether Samsung Electronics sank 2.68 percent and its chipmaking rival SK hynix declined 0.07 percent.Top carmaker Hyundai Motor retreated 3.92 percent and Hanwha Ocean, a major shipbuilder, tumbled 7.87 percent. Samsung Electro-Mechanics, an electronic components manufacturing affiliate of Samsung Electronics, fell 0.93 percent.The Korean won was trading at 1,530.2 won against the US dollar, down 3.2 won from the previous session, as of 9:15 a.m. (Yonhap)