U.S. Secretary of State Colin Powell telephoned Palestinian leader Yasser Arafat Wednesday to press him for an explanation of the ship intercepted by Israeli forces last week in the Red Sea, laden with weapons that Israel says were bound from Iran to the Palestinian Authority.

Administration officials have said they find Israel's account of the ship incident "credible" and there is increasing impatience here with what is said to be, thus-far, an unsatisfactory response from Mr. Arafat.

State Department spokesman Richard Boucher said, in the phone call to the Palestinian leader, Secretary Powell reminded him of the seriousness the United States attaches to the arms-smuggling affair and the "urgent need" for a full explanation. "The introduction of this kind of arms shipment into the region offers a serious potential for escalation," he added. "It's a real concern of the United States. It should be a real concern of all in the region. And we need to look into this matter and do something about. We've made it quite clear that Chairman Arafat needs to do something about preventing these kinds of shipments and dismantling the groups, organizations or people that are involved."

Mr. Boucher said the Palestinian leader reiterated to Secretary Powell that neither he nor the Palestinian Authority was involved, and that there would be a full investigation.

As he spoke, senior State Department officials were discussing the smuggling case with a team of Israeli military intelligence officials.

The Bush administration, meanwhile, strongly condemned the attack early Wednesday by the Palestinian militant group Hamas on an Israeli army post near the Gaza strip, which killed four Israeli soldiers and also left two Hamas gunmen dead.

White House spokesman Ari Fleischer said the attack was "particularly disturbing" since it came at a time of relative quiet, when the United States has working to help the parties achieve a durable peace.

He said the Hamas operation, though aimed at Israeli soldiers, was also a direct attack on Mr. Arafat's authority and said President Bush believes it is incumbent on the Palestinian leader to take immediate steps to "arrest terrorist leaders and dismantle the terrorist network" in the region.