Six US troops killed in Afghanistan as Taliban gains strength

"Our heartfelt sympathies go out to the families and friends of those affected in this tragic incident, especially during this holiday season," said a statement by U.S. Army Brig. Gen. William Shoffner, the head of public affairs at NATO's Resolute Support base in the Afghan capital, Kabul.

A New York police officer, Detective Joseph Lemm, was among those killed, said the city's Police Commissioner William Bratton. Lemm served in the U.S. National Guard and, while a member of the police force, he was deployed twice to Afghanistan and once to Iraq. He leaves behind a wife and three children.

It was the largest attack on foreign troops in four months. On Aug. 22, three American contractors with the Resolute Support base were killed in a suicide attack. On Aug. 7 and 8, Kabul was the scene of three insurgent attacks within 24 hours that left at least 35 people dead. One of the attacks, on a U.S. special operations forces base outside Kabul, left one U.S. service member and eight Afghan civilian contractors dead.

In the year since the international drawdown, the Taliban insurgency has intensified. Although the combat mission ended last year, about 9,800 U.S. troops and almost 4,000 NATO forces remain in Afghanistan. They have a mandate to train, assist and advise their Afghan counterparts, who are now effectively fighting a battle-hardened Taliban alone.

Monday's attack came as Taliban gunmen and government forces battled for control of a strategic district in Helmand after it was overrun by insurgents, delivering a serious blow to the government's thinly spread and exhausted forces.

Mohammad Jan Rasulyar, Helmand's deputy governor, said insurgents took control of Sangin district late Sunday.

Rasulyar took the unusual step of alerting Afghan President Ashraf Ghani to the dire security situation and requesting urgent reinforcements through an open letter posted on Facebook on Sunday, saying that he had not been able to make contact with him through other means.

"We had to take to social media to reach you, as Helmand is falling into the hands of the enemy and it requires your immediate attention," Rasulyar wrote in his post.

On Monday, Defense Ministry spokesman Dawlat Waziri said Afghan army commandos and special forces arrived in Sangin to push a counteroffensive. He told reporters the Afghan air force conducted 160 combat and transport flights over Sangin in the past 48 hours.

Helmand is an important region for the Taliban because it produces most of the world's opium, a crop that helps fund the insurgency.

Sangin has bounced in and out of Taliban control for some years, and fighting there has produced some of the most casualties among Afghan and international forces in 14 years of war.

British forces saw intense fighting there at the height of the war in 2006 and 2007. The U.K. lost more than 450 troops during its combat mission in Afghanistan — more than 100 of them in Sangin.

In 2008 a battalion of U.S. Marines arrived in Helmand, followed a year later by the first wave of President Barack Obama's surge effort against the Taliban, consisting of 11,000 Marines who conducted operations across the province.

The head of Helmand's provincial council, Muhammad Kareem Atal, said that about 65 percent of Helmand is now under Taliban control. "In every district either we are stepping back or we are handing territory over to Taliban, but still, until now, no serious action has been taken," he said, referring to a perceived lack of support from the capital.

Districts across Helmand — including Nad Ali, Kajaki, Musa Qala, Naw Zad, Gereshk and Garmser — have been threatened by Taliban takeover in recent months. Insurgents are believed to be dug in on the outskirts of the provincial capital, Lashkar Gah.

Taliban fighters, sometimes working with other insurgent groups like the Islamic Movement of Uzbekistan, have managed to overrun many districts across the country this year and staged a three-day takeover of the major northern city of Kunduz. They rarely hold territory for more than a few hours or days, but the impact on the morale of Afghan forces and civilians is substantial.