The US wants Israel to explain plans to build new homes in the West Bank, which were announced days after Washington urged an end to settlement expansion.
West Bank settlement expansion has drawn censure from the US
Israel said on Monday that it expects work to begin soon on 50 new homes in the northern West Bank town of Elkana.
The proposal comes days after President Bush warned Israeli Prime Minister Ariel Sharon to halt any such building.
Mr Sharon has also said he favours delaying until mid-August Israel's planned withdrawal from the Gaza Strip.
He wants to avoid the move overlapping with a Jewish mourning period marking the destruction of the biblical temples.
The pullout of all 8,000 Israeli settlers had been due to start on 20 July, but now Mr Sharon wants to delay it by three weeks until 16 August.
No action specified
The international community considers all settlements in Gaza and the West Bank, including East Jerusalem, as illegal under international law. Israel disagrees.
White House spokesman Scott McClellan said the US "will be seeking clarification from the government of Israel" over the plan for new homes in Elkana.
"Israel should not be expanding settlements," he said.
The Israeli authorities invited companies to bid for the contract to build the new houses.
An official said construction of the homes could start in eight to 12 weeks.
At a meeting with Israeli Prime Minister Ariel Sharon last week, President Bush said the expansion of West Bank settlements - particularly in East Jerusalem - violated the "roadmap" peace plan.
"I told the prime minister of my concern that Israel not undertake any activity that contravenes roadmap obligations or prejudices final status negotiations," he said.
He did not specify what, if any, action might be taken against Israel if it construction continued.
Mr Bush also praised Prime Minister Sharon for spearheading the plan to withdraw settlers and soldiers from Gaza this year.