South Korea's stock market led declines in Asian equities on Monday amid a sharp sell-off after tit-for-tat strikes between the United States and Iran sent oil prices soaring, raising widespread concerns about energy security and global supply chains.

South Korea's KOSPI index plunged 5.6% to 7,060.69 points, driven by steep losses among tech giants; SK Hynix memory chip shares tumbled 10.6% (erasing its record gains on Wall Street on Friday of 13%), while Samsung Electronics fell 6.7%.

Oil rises again

In energy markets, oil prices jumped as trading resumed, with benchmark Brent crude rising 3.9% to $78.96 a barrel, and US West Texas Intermediate crude climbing 4% to $74.26 a barrel.

The rise came hours after the US Central Command announced a new round of strikes on targets inside Iran, saying they aimed to undermine Tehran's ability to attack commercial vessels in the Strait of Hormuz.

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Asian and US stocks in the red

The downturn spread to other global and Asian markets as follows:

Tokyo: Japan's Nikkei 225 index fell 1.1% to 67,786.86 points.

China: The Shanghai Composite Index fell 1.2%, while Hong Kong bucked the trend with the Hang Seng Index rising slightly by 0.1%.

Australia: The S&P/ASX 200 index fell 0.3%.

In US markets, futures for major indexes fell collectively, with the Nasdaq Composite down 1%, the S&P 500 down 0.4%, and the Dow Jones Industrial Average down 0.3%.