RAMALLAH, West Bank (AP) -- Israeli tanks began withdrawing from the West Bank city of Ramallah Thursday night, just hours after the arrival of U.S. mediator Anthony Zinni on a mission to achieve a cease-fire.

The United States has been exerting pressure on Israel to pull its soldiers from Palestinian cities.

Dozens of Israeli tanks rolled into Ramallah on Tuesday as part of the largest-scale military operation since the 1982 invasion of Lebanon. The Israeli military chief has said 20,000 soldiers were deployed in the West Bank and Gaza Strip, in response to a string of attacks on Israelis by Palestinian militants.

Israeli Defense Minister Binyamin Ben-Eliezer ordered a gradual pullback of troops from Ramallah as Zinni arrived.

But the Bush administration said that was not enough.

"We do expect a complete withdrawal from Palestinian-controlled areas, including Ramallah, and the other areas the Israel Defense Force recently entered," State Department spokesman Richard Boucher said. He also called on Arafat "to do more to stop the groups that carry out violence."