A sell sidecar was triggered on South Korea\'s main stock market on May 18 after the KOSPI slid more than 3 percent in early trade. Korea Exchange said it activated a temporary halt on program trading sell orders at 9:19:22 a.m. The mechanism is designed to limit spillover from sharp futures declines into the spot market. It triggers when KOSPI 200 futures fall at least 5 percent for 1 minute and suspends program sell orders for 5 minutes.

South Korean shares surged early on Tuesday on expectations of easing Middle East tensions and a temporary truce involving the United States and Iran. The KOSPI rose more than 5 percent, while the Kosdaq gained more than 4 percent. Buying sidecar mechanisms were triggered in both markets, temporarily halting the effectiveness of program buy orders. Institutions and foreigners were net buyers, while individuals were net sellers.