The United States military has suspended its blacklisting of Afghanistan's largest private airline Kam Air after the government promised an investigation into claims that it was trafficking opium. The US Central Command made the decision because "it is an appropriate, logical course of action at this time for the sovereign Afghan government to conduct a full investigation of Kam Air", US Forces-Afghanistan said Monday. In return, the US "will support the Afghan government's investigation by providing evidence and documents as required", it said. The US had banned the airline from its list of potential military contractors, claiming the company was conveying "bulk" quantities of opium to neighbouring Tajikistan, the Wall Street Journal revealed last week. The impoverished Central Asian country is regarded as a key transit route used by drug smugglers. The airline rejected the allegation and the government demanded proof of drug smuggling from the US. "The Afghan government welcomes CENTCOM's decision to return its business relations with Kam Air to normal," a government spokesman said. "We believe this was the right decision to take. At the same time the Afghan government remains committed to fully investigating this whole matter, including through the examination of any and all evidence from US CENTCOM." Ninety percent of the world's opium is produced is Afghanistan, according to the UN Office on Drugs and Crime. The trade fuels corruption in the country, and poppy farmers are also taxed by Taliban militants who use the cash to help fund their insurgency against the Kabul government and US-led NATO forces.