By Michele Kambas NICOSIA (Reuters) - Two firefighters were killed and a third was critically injured while tackling one of the largest forest fires in Cyprus in years. The blaze, possibly started by an attempt to burn dry stubble, broke out on Sunday in the foothills of the Troodos mountain region of the eastern Mediterranean island. It has been fanned by high winds and scorching temperatures, hampering efforts by firefighters backed by water bomber aircraft from Greece and Israel and helicopters from the British military bases in Cyprus.