* Clear risk of alliances between Islamic State, locals * Italy willing to take lead role within UN framework * Boat arrivals up 60 pct so far this year ROME, Feb 18 (Reuters) - Italy called on Wednesday for urgent international action to halt Libya's slide into chaos, and pledged it was ready to help monitor a ceasefire and train local armed forces. The U.N. Security Council is due to meet later on Wednesday to discuss Libya, where two rival governments, each backed by former rebels who toppled Muammar Gaddafi in 2011, are battling for power. The growing danger became apparent on Sunday when Islamic State released a video showing the beheading of 21 Egyptian Coptic Christians in Libya. Foreign Minister Paolo Gentiloni told parliament that possible alliances between local militias and IS militants, inspired by counterparts in Syria and Iraq, risked destabilising neighbouring countries.