Dollar wavers amid renewed Iran attacks, yen slides on pensions doubts

Oil prices rose, with Brent crude futures up 3.5% at $78.65 a barrel.

The dollar index, which tracks the currency against six peers, was last down 0.15% at 100.9.

"The dollar was obviously the big winner from the war last time. But it's starting from a pretty different point this time, having strengthened quite a lot and there already having been a fairly lasting repricing of the Fed outlook," said Thomas Mathews, head of markets for Asia Pacific at Capital Economics in Wellington.

"It's not clear to me the greenback would gain as much this time if the situation continued to worsen, which I think is probably reflected in trade so far."

Fed funds futures are pricing an implied 50% probability of two or more rate hikes by the time of the U.S. central bank's December meeting, up slightly from Friday, according to the CME Group's FedWatch tool.