KABUL (Reuters) Afghan insurgents are being trained inside Iran and given weapons to fight security forces, the commander of US and NATO forces said on Sunday, joining a rising drumbeat of criticism of Irans role in the country. General Stanley McChrystal said coalition forces were working to stop Iran from giving material help to the Taliban who have stepped up the campaign to force foreign forces out of Afghanistan in a nine-year conflict. The training that we have seen occurs inside Iran with fighters moving inside Iran, he said at a news conference in response to a question on Irans influence. The weapons that we have received come from Iran into Afghanistan. The United States, battling a Taliban insurgency at its worst, has frequently accused Iran of providing some assistance to insurgents in Afghanistan, although Washington says it has not been nearly as important a factor as in Iraq, Irans other neighbour, where US troops are waging war. In March, Chairman of the Joint Chiefs of Staff Admiral Mike Mullen said there had been a significant shipment of Iranian arms to fighters in the southern province of Kandahar. ^ US forces are preparing for an offensive in Kandahar, the spiritual capital of the Taliban, this summer in what is seen a turning point in the war to force the insurgents to the negotiating table for a settlement of the conflict. Iran denies supporting militant groups opposed to Afghan President Hamid Karzais government, and says it has a stake in the security of the neighbouring state. Tehrans economic influence in Afghanistan has grown rapidly in recent years, especially in the West, where cross-border trade is brisk. McChrystal said Iran, as a neighbour, had natural interests in Afghanistan and to a certain extent the assistance and interaction it provided was healthy. There is however clear evidence of Iranian activity, in some cases of providing weapons and training to the Taliban that is inappropriate, he said.