KABUL, Afghanistan — When Afghanistan’s President Ashraf Ghani took office, he ushered in a period of hope for the country’s traumatized and war-weary people that decades of violence would soon end. But just one year later, British troops are deploying to help beleaguered Afghan troops regain control of a strategically important district in poppy-producing Helmand province, and many Afghans now believe the Taliban are winning.

The development came a day after a Taliban suicide bomber killed six U.S. troops near a major military base — the deadliest day for American troops in the country since 2013.

A British Ministry of Defense statement late Monday said “a small number of U.K. personnel” have been deployed to Helmand “in an advisory role.” The U.K. has 450 troops in Afghanistan as part of NATO’s training mission.

Fighting raged between Taliban and Afghan forces in Helmand’s Sangin district, where an official said the district’s army base was the only area that had not fallen to the Taliban. He spoke on condition of anonymity because he was not authorized to speak to the media.

The spokesman for the Helmand governor, Omar Zwaq, said government troops were able to deliver supplies to those holed up inside mid-afternoon Tuesday. But, he added, there was no let-up in the fight for Sangin.

Taliban spokesman Qari Yousaf said the siege continued “and the government will soon announce their defeat.”

Helmand is important to the Taliban. The lush southern province is home to endless poppy fields and the source of almost all the world’s opium, which helps fund the insurgency. The head of Helmand’s provincial council, Muhammad Kareem Atal, said about 65 percent of Helmand is now under Taliban control.

Security has worsened across the country as the Taliban test the mettle of Afghan security forces following the end of the international combat mission last year. While they don’t typically hold any territory they win for more than a few hours or days, the Taliban have dealt a massive blow to the confidence of the over-stretched Afghan forces, who are fighting the insurgency alone for the first time. Officials have said casualties, as well as attrition and desertion, have taken a toll on numbers of government forces, while the Taliban strength seems never to diminish.

There are currently about 13,000 foreign troops in Afghanistan, including 9,800 Americans, with a mandate to “train, assist and advise” their Afghan counterparts. That’s compared to 140,000 foreign troops at the peak of combat operations in 2011.

Officials see no traditional winter slowdown in the insurgents’ quest to overthrow the Kabul government, especially in the warmer southern provinces of Helmand and Kandahar. They expect tough fighting in 2016 as what the Pentagon last week called an “invigorated Taliban” steps up its fight.

At the same time, Ghani’s government appears paralyzed by indecision and a lack of political intelligence that sees him use public appearances to deliver lectures but remains incapable of permanently filling vital security posts such as defense and intelligence, both of which are run by acting ministers.

This week, a senior official said he was unable to reach Ghani and resorted to Facebook to warn of the Taliban’s encroachment on Sangin. Hundreds of Afghan security forces have been killed fighting the Taliban across the province in the past six months, Helmand’s deputy governor Mohammad Jan Rasulyar said.