The U.S. Army has issued an apology for dumping a toxic chemical into the Han River.

General Daniel Petrosky, the Commander of the 8th U.S. Army in South Korea, conveyed a letter of apology to Seoul Mayor Koh Gun Thursday afternoon. In the letter, General Petrosky promised to take steps to ensure such dumping will not occur again.

He also promised to punish those responsible for the release of formaldehyde after investigations.

This is the first time a top U.S. military commander has apologized for incidents involving American troops. 37,000 U.S. service members are stationed in South Korea.

U.S. military and embassy officials in Seoul have faced pressure from the Seoul government and civic groups to apologize for the incident, which fanned anti-Americanism. Earlier this week, the Foreign Affairs and Trade Ministry expressed South Korea's regret over the secret dumping of the toxic chemical in February.

Thousands of South Koreans took to the streets last week after the U.S. military acknowledged it had dumped formaldehyde into the Han River, a major source of drinking water for Seoul's 12 million people.

The South Korean media criticized the chemical dumping as "disregarding the South Korean people."