The United States believes North Korea has suffered "several hundred" troop casualties during combat alongside Russian forces against Ukraine, a Pentagon spokesperson said Thursday, noting that the figure could go up.

Pentagon press secretary Major Gen. Pat Ryder made the remarks after South Korea's National Intelligence Service told lawmakers in Seoul that at least 100 North Korean troops, who were dispatched to Russia, were killed in action (KIA), with the number of injured North Korean troops estimated to reach some 1,000.

"We continue to observe and assess. I would say at this stage, it's our assessment that several hundred DPRK forces have been or several hundred casualties that would range from killed in action to wounded," Ryder told a press briefing, referring to North Korea by its official name, the Democratic People's Republic of Korea.

"I am not going to have a breakdown for you in terms of KIA versus wounded ... As they engage in combat with the Russians, we certainly would anticipate that those numbers will go up," he added. (Yonhap)