South Korea's KOSPI climbed nearly 5 percent in early trading on June 15 to reclaim the 8,500 level. News that the United States and Iran agreed to end the war, strong performance in U.S. stocks in the previous session and gains in semiconductor shares were seen as lifting investor sentiment. The Kosdaq was also strong, trading above 1,000.

As of 9:12 a.m., the KOSPI was up 400.92 points, or 4.94 percent, at 8,524.54. The index opened up 402.50 points, or 4.95 percent, at 8,526.12 and climbed as high as 8,552.31 early on.

The KOSPI closed at 8,123.62 on June 12 and moved above 8,500 shortly after the open on June 15. It started higher reflecting strength in KOSPI 200 night futures, and buying spread across heavyweight sectors including semiconductors, electrical and electronics, autos and finance.

A buy sidecar was also triggered on the main bourse during the sharp rise. Korea Exchange disclosed that it activated a buy sidecar in the KOSPI market at 9:06:02 a.m. At the time, the KOSPI 200 futures price was up 66.00 points, or 5.07 percent, from the previous session at 1,365.85.

A buy sidecar is triggered when the KOSPI 200 futures price stays up at least 5 percent from the previous closing level for 1 minute. After it is triggered, the validity of program buy orders is suspended for 5 minutes.

The KOSPI buy sidecar was triggered for a second straight session following June 12. The KOSPI has continued a volatile pattern this month, with four buy sidecars and three sell sidecars over nine sessions.

By investor type, individuals and institutions were net buyers of 293.0 billion won and 117.0 billion won, respectively. Foreigners were net sellers of 468.5 billion won.

Most top market-cap stocks were higher. Samsung Electronics was trading up 16,000 won, or 4.96 percent, at 338,500 won. SK Hynix was up 150,000 won, or 6.98 percent, at 2.30 million won.

Elsewhere, SK Square was up 3.83 percent and Samsung Electro-Mechanics rose 13.48 percent. Hyundai Motor gained 5.44 percent, LG Energy Solution rose 3.63 percent, Samsung Life gained 6.87 percent, Samsung C&T rose 10.53 percent and HD Hyundai Heavy Industries climbed 9.38 percent.

The Kosdaq was also higher. At the same time, it was up 19.12 points, or 1.86 percent, at 1,048.17. After reclaiming 1,000 last week, it extended gains on the day to rise above 1,040.

In the Seoul foreign exchange market, the won was quoted at 1,504.60 per dollar, up 10.10 won from the previous session. As the rate fell to the low 1,500s, supply-demand pressure on the local stock market also appeared to ease somewhat.

The securities industry expects the local stock market to remain volatile this week as it digests external factors and major events.

Han Ji-young (한지영), a researcher at Kiwoom Securities, said the KOSPI this week will be affected by expectations for the final signing of a U.S.-Iran ceasefire MOU, the June FOMC and BOJ meetings, key indicators such as U.S. May retail sales and industrial production, changes in SpaceX share prices and supply-demand conditions, and whether foreigners' net buying of domestic shares continues.