South Korea's primary stock market index tumbled more than 3% Thursday as investors tracked US-Iran peace talks, with the White House signaling progress despite Iran's initial rejection of a 15-point plan, while Tehran called Washington's tone a sign of failure.

The benchmark Korea Composite Stock Price Index or Kospi fell by 181.75 points, or 3.2%, to finish at 5,460.46. The Kosdaq also decreased by 22.91 points, or 2%, to end at 1,136.64.

In economic news, the Bank of Korea plans to issue monetary stabilization bonds (MSBs) totaling around 6 trillion won in April 2026. Out of this, 5.5 trillion won will be offered through competitive bidding, and 400-500 billion won through fixed-rate tenders.

In corporate news, GS Engineering & Construction (KRX:006360) secured the Urban Public housing complex project on the west side of Ssangmun station from Korea Land & Housing Corporation, the construction company said in a Thursday filing with the Korea Exchange.

The contract, valued at 583.6 billion won, is valid until Feb. 28, 2033.

Shares of GS Engineering & Construction fell more than 4% at market close.

In other news, Alteogen (KOSDAQ:196170) on Thursday said it agreed to grant Biogen (NASDAQ:BIIB) rights to its ALT-B4, a proprietary recombinant human hyaluronidase developed using Alteogen's Hybrozyme platform technology.

Under the deal, Biogen will have exclusive rights to develop and commercialize subcutaneous (SC) formulations for two biologic products based on ALT-B4.

Alteogen will receive an upfront payment of $20 million and is eligible for $10 million upon the start of the second product development. It is also entitled to up to $559 million in milestone payments for two products and sales-based royalties. Biogen holds an option for a third product.

Shares of Alteogen added over 6% at market close.