Israeli troops shot and killed two Palestinian men who tried to stab soldiers at a checkpoint in the occupied West Bank yesterday, the Israeli military said, part of a wave of violence now in its fourth month. Palestinian stabbing, car-ramming and shooting attacks have killed 21 Israelis and a US citizen since Oct. 1. Israeli forces or armed civilians have killed at least 139 Palestinians, 89 of whom authorities described as assailants. Most others have been killed in clashes with security forces. Also stoking the violence has been Muslim opposition to increased Israeli visits to Jerusalem's al Aqsa mosque complex.