General Stanley McChrystal, commander of U.S. and NATO forces in Afghanistan, said a thorough investigation would be launched into the airstrike that killed 21 civilians on Sunday. (Kirsty Wigglesworth/Associated Press)

The commander of U.S. and NATO forces in Afghanistan went on national television Tuesday to apologize for a deadly airstrike, an extraordinary attempt to regain Afghans' trust while a mass offensive continues against the Taliban in the south.

In a video translated into the Afghan languages of Dari and Pashto and broadcast on Afghan television, a stern Gen. Stanley McChrystal apologized for the strike in central Uruzgan province that Afghan officials say killed at least 21 people. The video was also posted on a NATO website.

"I pledge to strengthen our efforts to regain your trust to build a brighter future for all Afghans," McChrystal said in the video. "I have instituted a thorough investigation to prevent this from happening again."

Sunday's attack by NATO jets on a convoy of cars was the deadliest attack on civilians in six months and prompted a sharp rebuke from the Afghan government. McChrystal apologized directly to President Hamid Karzai shortly after the incident.

NATO said McChrystal made a similar apology via video this past fall when U.S. pilots bombed two hijacked fuel tankers near the northern town of Kunduz. Afghan leaders estimated that 30 to 40 civilians were killed.

10th day of fighting in Helmand province

The civilian deaths occurred as 15,000 NATO, U.S. and Afghan soldiers were in their 10th day of fighting insurgents in the town in Helmand province. A Romanian soldier was killed Tuesday and another was wounded in a bombing in southern Afghanistan unrelated to the offensive, Romanian officials said.

Two U.S. Marine battalions, accompanied by Afghan troops, pushing from the north and south of the insurgent stronghold of Marjah finally linked up after more than a week on Tuesday, creating a direct route across the town that allows convoys to supply ammunition and reinforcements.

Although the airstrike was not related to the Marjah offensive, civilian casualties undermine NATO's goal of turning back the Taliban and restoring the Afghan people's confidence in their own government — one of the main objectives of the southern operation that hopes to rout the Taliban, set up a local government and rush in aid.

In Berlin, Richard Holbrooke, the U.S. special envoy for Afghanistan and Pakistan, said civilian casualties were "great tragedies," but stressed that Gen. McChrystal has done the utmost to avoid civilian deaths, noting especially the new guidelines restricting airstrikes.

The alliance said its planes fired on what was thought to be a group of insurgents in Uruzgan province on their way to attack NATO and Afghan forces. Interior Ministry spokesman Zemeri Bashary said the airstrike hit three minibuses of civilians, which were traveling on a major road near Uruzgan's border with Day Kundi province.

Sporadic fighting continued Tuesday as entrenched Taliban units appeared to have regrouped in a heavily defended stronghold to the north.

Other areas were calm enough, however, that police were able to hand out aid to residents. The provincial governor joined Afghan officers in piling bags of rice and tea onto blankets and distributing them in central Marjah.