FORWARD OPERATING BASE FRONTENAC, Afghanistan, (Reuters) - US Secretary of Defence Robert Gates told troops in southern Afghanistan on Tuesday they would soon be part of a decisive phase in the war - an operation to impose control over the Taliban heartland of Kandahar province. NATO is sending thousands of extra troops to Kandahar over the next few months as part of plans to restore control over Kandahar. Thousands of Americans arrived in the area last year, bolstering a force of about 3,000 Canadians and taking heavy casualties. US commanders say much of the area remains in the hands of an increasingly potent Taliban insurgency. You all have had a very tough tour, Gates told troops with a Stryker brigade at Forward Operating Base Frontenac, about 48 km north of Kandahar city. Twenty-two troops have been killed and 62 wounded in the area since July last year. You came to an area that was totally controlled by the Taliban. You bled for it, Gates said. Here in the environs of Kandahar, youre in an area that once again is going to be an important part of the decisive phase of this campaign. Once again, you will be the tip of the spear, he said. General Stanley McChrystal, commander of US and NATO forces in Afghanistan, has said the Kandahar operation will be gradual, without a single big assault like the one last month against the Taliban stronghold of Marjah in neighbouring Helmand province. About 85 percent of the 30,000 extra troops sent by Obama have yet to arrive. Most of the new combat power will be deployed in the next few months in and around Kandahar. By the end of the traditional summer fighting season, US and NATO forces hope to have restored full government control over Kandahar, the countrys second-largest city, and the agricultural districts around it. Lieutenant Colonel Jonathan Neumann, battalion commander of the Stryker unit at Frontenac, said his forces were already involved in preparing the area for the upcoming offensive and were working to keep roads open for trade in and out of the city. I think we already are the tip of that spear, Neumann said in a briefing with reporters. Meaning that operations in the Kandahar province are already setting the stage.