The officials said on Tuesday they wanted to know whether Shaul Mofaz had been speaking personally or was reflecting the view of Ariel Sharon's government when he made the threat in a radio interview.
"Before we respond, we need to know the context," said one official, speaking anonymously. Another official said US diplomats in Israel were making inquiries about the remarks but could not say to whom the questions had been addressed.
Mofaz told Israeli military radio the government would now consider expelling Arafat because he was an obstacle to the peace process.
"We made a historic mistake by not expelling him two years ago but we’re going to address this issue in the short-term, without doubt before the end of the year," he said.
Pressure on Arafat
State Department spokesman Richard Boucher said Washington was aware of Mofaz's remarks and the US position on Arafat - declared an obstacle to peace by President George Bush in June 2002 - had not changed.
"Arafat is part of the problem at this point and is not helping to bring a solution," he said.
Pressed on the expulsion threat, he said the last time the question of Arafat's expulsion had arisen, the US had opposed the idea and had been pleased when Israel said they did not plan to do so.
Arafat has been effectively confined to his headquarters in the West Bank town of Ramallah by the Israeli army for the past 20 months.
In recent weeks, the US has ramped up pressure on Arafat to turn over the entire Palestinian security apparatus to Prime Minister Mahmud Abbas in order to rein in militant groups like Hamas and Islamic Jihad.