The top US general in Europe has warned that Russia may now be arming militants in Afghanistan, as an Afghan town was captured by the Taliban after more than 100 British soldiers died trying to defend it.

The strategic district of Sangin in Helmand province was the deadliest battlefield for UK forces in Afghanistan. But the town fell early on Thursday morning as Taliban forces continued a year-long offensive to extend their reach in southern Afghanistan.

The Afghan government said it would recapture the town but it was not clear if it had the forces necessary.

The setback came as the top US general in Europe warned that Russia may now be arming the militants. "I've seen the influence of Russia of late - increased influence in terms of association and perhaps even supply to the Taliban," Curtis Scaparrotti, Nato's Supreme Allied Commander Europe, told a Senate hearing in Washington.