The leader of the US House of Representatives said on Tuesday that he's puzzled by reports that Israel spied on negotiators in the closed-door talks over Iran's nuclear program - a claim that Israeli officials deny.

"I'm baffled by it," Speaker John Boehner told reporters about the report that comes at a time of strained relations between the US and Israel.

At a news conference on Afghanistan, President Barack Obama said he did not want to comment on other nations' intelligence, but said, "We have not just briefed Congress about the progress, or lack thereof, but we also briefed the Israelis and our other partners in the region".