JERUSALEM -- Israel pulled out of two dozen small West Bank towns and villages Thursday but swept into others and rounded up more Palestinian men despite U.S. calls and international pressure to end the 2-week-old campaign to root out militants.

Israel's army says 4,185 Palestinians have been detained in the operation -- nearly half of them in the past two days as fighters in the key northern West Bank cities of Jenin and Nablus, their numbers depleted in battle, ran out of ammunition and surrendered.

Among those in custody were 121 Palestinians who had been on Israel's wanted list, the army said.

Secretary of State Colin Powell arrived in Israel Thursday night and was expected to meet with both Israeli Prime Minister Ariel Sharon and Palestinian leader Yasser Arafat, who has been kept a virtual prisoner by Israel in his besieged compound in Ramallah.

On Thursday, Sharon acknowledged the fighting was causing the United States difficulties but refused to call a halt to the incursion.

There has been rising anti-American sentiment throughout the Arab world in response to Israel's offensive, launched two weeks ago to crush Palestinian militias after a series of deadly attacks on Israeli civilians.

The Americans have problems in the region, Sharon said, "that's true, but I informed them that our activity will continue -- and it will continue."

Powell visit

The United States, along with the United Nations and European leaders, has demanded an immediate Israeli pullout from the West Bank. Powell was visiting the region in an attempt to secure a cease-fire and restart peace talks.

In what appeared to be a gesture ahead of Powell's arrival, Israeli forces withdrew from about two dozen small towns and villages. But in raids early Thursday, they entered the West Bank towns of Dahariyah and Bir Zeit and the Ein Beit Hilmeh refugee camp. Later, they pulled out of Bir Zeit after detaining about 300 people, mainly students in the university town.

The White House raised no objection to the pace of Israel's response to President Bush's pleas.

"The withdrawals he called for are continuing," White House spokesman Ari Fleischer said.