American mediator Anthony Zinni reported some headway in security talks with Israel and the Palestinian Authority, but Vice President Dick Cheney's return to the Middle East to see Yasser Arafat remained in limbo.

"A meeting could happen if and when Chairman Arafat performs, does what he's supposed to do," President Bush said Friday at a news conference in Monterrey, Mexico, where he was attending an international meeting.

Bush said Zinni was "trying to determine whether or not [Arafat] is going to do what he said he would do."

Contingency preparations for a Cheney-Arafat meeting in Egypt proceeded, but it depends on the Palestinian leader agreeing to U.S. terms for a cease-fire, administration officials underscored.

"As of now, the conditions have not been met," a White House spokesman, Sean McCormack, said.

On Capitol Hill, Sen. Dianne Feinstein, D-Calif., organized a congressional drive to stop the Cheney trip.

Feinstein rounded up 51 senators to join her in a letter to President Bush. The letter said "there is no evidence, on the ground, that Mr. Arafat is willing to do what is necessary to help bring peace to Israel and his people."

And yet, they said, Cheney has offered to return to the region to see Arafat.

The senators also told the president that they supported the Zinni mission but hoped the retired Marine general "makes clear that the United States will not deal with those who do not live up to their commitments."

In a third suicide bombing in three days, a Palestinian man intercepted by border guards, blew himself up at a military checkpoint on the West Bank.

Truce talks resumed after Zinni complained to Arafat that he had not done enough to prevent attacks. Another meeting was set for Sunday.

Zinni reported to Assistant Secretary of State William Burns there was "some headway" toward a cease-fire, said a U.S. official, speaking on condition of anonymity.

The State Department, meanwhile, welcomed a promise by Arafat to end attacks on Israel.

"We expect that he and the Palestinian Authority will move immediately to reinforce these words with definitive action. It's that definitive action and results that we're looking for," spokesman Philip Reeker said.

In an interview for PBS' NOW With Bill Moyers, Marwan Zaloum, a commander in the Al Aqsa Brigades, which claimed responsibility for Thursday's bombing, pledged: "We will continue until we vanquish the occupation and until the creation of the Palestinian state. This is the message that the whole world has to understand."

Secretary of State Colin Powell, traveling with Bush in Mexico, has kept in telephone touch with Arafat.

Powell told him "he must punish the leaders of organizations responsible for recent attacks, making sure those responsible are brought to justice," Reeker said.