JERUSALEM?On the eve of a new U.S. mediation mission, Ariel Sharon’s advisers said Wednesday that the Palestinians have not yet met the prime minister’s condition for a formal truce?a week without attacks on Israelis.

The United States does not fully back Sharon’s demand?U.S. officials have said privately that a few days of calm are sufficient?and the prime minister appeared set for possible friction with U.S. envoy Anthony Zinni.

Zinni is returning to the region Thursday, after a flare up in violence, including a series of deadly attacks on Israeli civilians by Palestinian militants, derailed his first three-week mission in December.

This time, Zinni is expected to stay for four days.

The level of violence dropped sharply after Palestinian leader Yasser Arafat announced Dec. 16 that he would work hard to enforce a truce with Israel. No Israelis have been killed since then.