UNITED NATIONS, Sept 10 (Reuters) - U.N. Secretary-General Antonio Guterres appealed on Friday for an injection of cash into Afghanistan to avoid an economic meltdown that would spark a "catastrophic" situation for the Afghan people and be a "gift for terrorist groups." His remarks come after his special envoy on Afghanistan, Deborah Lyons, warned the Security Council on Thursday that the freezing of billions of dollars in international Afghan assets to keep them out of Taliban hands would inevitably spark "a severe economic downturn." "At the present moment the U.N. is not even able to pay its salaries to its own workers," Guterres told reporters. "We need to find ways to avoid a situation that would be catastrophic for the people and, in my opinion, a source of instability, and an action, gift for terrorist groups still operating there," he said. Al Qaeda and the Islamic State"s Afghan affiliate, ISIS-Khorosan, are present in Afghanistan. Guterres said he had been speaking with International Monetary Fund chief Kristalina Georgieva, telling reporters it was essential to agree on waivers or mechanisms to get money into Afghanistan. The IMF has blocked the Taliban from accessing some $440 million in new emergency reserves. Much of the Afghan central bank"s $10 billion in assets are also parked overseas, where they have been frozen since the Taliban came to power last month. They are considered a key instrument for the West to pressure the Islamist group. Both Guterres and U.N. aid chief Martin Griffiths hope that international programs to get cash into war-torn Yemen could be replicated in Afghanistan. In Yemen, the U.N. children"s agency, UNICEF, makes monthly cash payments to some 1.5 million of the poorest families through a program funded by the World Bank. The United Nations is also working to ensure it can continue its humanitarian work in Afghanistan, where at least 18 million people - half the country"s population - already need help. "We are permanently engaging with the Taliban and we believe that the dialogue with the Taliban is absolutely essential at the present moment," Guterres said.