Gulabuddin Mangal, governor of Afghanistan's southern Helmand province, said the American military had better resources and finances to deal with insurgent violence in and around the town of Sangin.
US Marines took over responsibilities for Sangin in September, taking over from British troops who had fought there since 2006 and suffered more than 100 deaths - almost a third of the 342 casualties suffered by the UK since operations in Afghanistan began in 2001.
"By having the marines of the US, we have improved security now in some areas," Mr Mangal said.
American forces replaced the British allies under a reorganisation of international troops in Helmand. Some critics claimed the switch followed a pattern set in Iraq, when the Americans moved into regions around the southern city of Basra to shore up Britain's military efforts.
"Not many countries have the finances, logistics and equipment (of the US]," Mr Mangal said yesterday on a trip to Britain.
British officers insist the move out of Sangin was on tactical grounds, allowing US troops to cluster in the north of Helmand, while British and other troops focus on central and southern areas of the province.
Mr Mangal, who said he will meet with relatives of a British soldier killed in Helmand and visit the National War Memorial in Staffordshire during his trip to Britain, insisted that UK forces had achieved successes.
The governor said insurgent groups had been effectively dismantled in Helmand's Nad-e-Ali, Marjah, Nawar and Gereshk districts as a result of recent joint offensives between Afghan and international forces.
"The insurgents are not able to have ten or 15 people in their groups, this means they were broken into pieces and defeated," Mr Mangal said.
He said that he had now ordered his staff to use only roads - rather than helicopters - to access those areas in the future, to demonstrate the improved security.