Rwandan and Congolese troops have exchanged fire with Rwandan Hutu militiamen in eastern Congo, killing nine in the first fighting reported since an unprecedented joint military operation began this week, the UN said. The skirmish took place around Lubero, west of Lake Edward, late Saturday said UN peacekeeping spokesman Lt. Col. Jean-Paul Dietrich. The UN is not involved in the operation and no details were immediately available. Rwanda and Congo have been enemies for years, but the two neighbors suddenly changed tactics and began cooperating in an effort to disarm the rival militia groups each nation has backed as proxies. Eastern Congo has been wracked by violence since Rwanda's 1994 genocide spilled war across the border and Hutu militias who participated in the massacres of more than 500,000 mostly ethnic Tutsi civilians sought refuge in Congo.