KABUL - A roadside bomb killed a US soldier and wounded another when their patrol went to the assistance of Afghan troops in the southern province of Helmand, the NATO-led forces in Afghanistan said in a statement on Tuesday.

The province, a traditional stronghold of the Taliban and a major centre for the opium production, has seen fierce fighting in recent weeks. Taliban forces have made gains across Helmand in the past year, forcing government forces to abandon some bases and checkpoints in a bid to consolidate their defenses in and around key districts. Meanwhile, Afghanistan Tuesday welcomed the deployment of around 100 US troops to Lashkar Gah to help head off a potential Taliban takeover, the first major American deployment to the southern city since foreign forces withdrew in 2014.

Fighting has recently escalated in the southern opium-growing province of Helmand, with insurgents coming within a few kilometres of its capital Lashkar Gah, raising alarm that the city was at risk.

The Taliban have also closed in on Kunduz, the northern city which the insurgents briefly seized last year in their biggest military victory so far, leaving Afghan forces stretched on multiple fronts.

“This is a big effort by the Taliban. It’s probably the most serious push we’ve seen of the (fighting) season,” Brig Gen Charles Cleveland, spokesman for US-led NATO forces in Afghanistan, told reporters on Monday.

Cleveland said around 100 US troops had been deployed to Lashkar Gah, in what he called a “temporary effort” to train and advise local forces, although he refused to specify a time frame. “We do not believe that Lashkar Gah is about to fall,” he added.

The Afghan defence ministry welcomed the US reinforcements. “The (US) troops... are providing all the support necessary to our forces on the ground,” ministry spokesman Mohammad Radmanesh told AFP.

“We have enough Afghan troops on the ground in Helmand, but they need support and training from our international partners. We appreciate their presence alongside our forces.”

The turmoil convulsing Helmand, blighted by a huge opium harvest that helps fund the insurgency, underscores a rapidly unravelling security situation in Afghanistan.

Fighting has left thousands of people displaced in Helmand in recent weeks, sparking a humanitarian crisis as officials report food and water shortages.

NATO officially ended its combat mission in December 2014, but US forces were granted greater powers in June to strike at the insurgents as President Barack Obama vowed a more aggressive campaign.

The US intervention has fuelled the perception that foreign powers are increasingly being drawn back into the conflict as Afghan forces struggle to rein in the Taliban.

The fighting in Helmand comes as Afghan troops are stretched on several other battlefronts across Afghanistan - including eastern Nangarhar province where the Islamic State group is making inroads.