As many as 150 insurgent fighters have been killed since Sunday in a major offensive involving about 700 U.S. and Afghan troops along eastern Afghanistan's border with Pakistan, a senior military official confirmed to Fox News early Tuesday.
The U.S.-led operation was one of the largest yet in the region, officials told The Washington Post, who described the assault as "one of the most intense battles of the past year."
In a statement Sunday, NATO's International Security Assistance Force said more than 600 ISAF and Afghan troops were pursuing Al Qaeda and Taliban militants in Kunar and that "a number of insurgents" were killed.
Two American troops were also killed in the battle, according to ISAF.
The offensive was designed to flush out growing numbers of Taliban militants bidding to open up a second front in Kunar, as U.S.-led forces root out insurgents in southern Afghanistan, the Post reported.
"The Taliban know we are bringing our surge of forces, and they realize they can't just let that happen, so they are pursuing their own surge," Maj. Gen. John Campbell, the senior commander in eastern Afghanistan, told the newspaper.
The U.S.-led force in Kunar gave no prior warning of the offensive, unlike the onslaught in Marjah in southern Afghanistan earlier this year.
"We needed the element of surprise in that terrain," Colonel Andrew P. Poppas was quoted as saying.
U.S. and Afghan troops were flown in before dawn Sunday on Black Hawk helicopters and seized mountainous ground in Kunar's Marawara district, but soon came under attack from as many as 200 insurgents, the newspaper reported.
"Once the battle began, others from the area tried to maneuver into the area," Poppas was quoted as saying. "This was a tough fight."
The heaviest fighting subsided by Monday morning. U.S. and Afghan forces are now trying to restore government authority in Marawara's main village.
"The tough part is still ahead," Poppas said.
NewsCore contributed to this report.