The United States "will not waver" in its efforts to implement the so-called roadmap to peace in the Middle East, Secretary of State Colin Powell has said. He urged Israel and the Palestinians to halt the tit-for-tat attacks that have strained efforts for peace almost to breaking point in the week since the roadmap was launched. Powell was speaking as John Wolf, the US envoy whose stated task is to "monitor and implement" the roadmap, arrived in Israel. Wolf is scheduled to meet Israeli officials in the West Bank on Sunday, followed by meetings with Israeli Prime Minister Ariel Sharon and Palestinian officials over the next few days.