Reports from the US suggest Washington has been asked to speed up a shipment of precision bombs sold as part of a deal with Israel last year.
According to a report in the New York Times, Israel made the request after it began its air assault on Hezbollah targets in Lebanon 12 days ago.
The weapons, including five-tonne laser-guided bombs, are part of a sale signed last year.
Unnamed US officials say the request to speed up delivery is unusual.
The disclosure is likely to anger Arab governments because of the appearance that the United States is actively aiding Israel at such a sensitive time.
Precision-guided missiles are playing a key part in Israel's military strategy, which has included attempts to destroy bunkers it says are used by Hezbollah.
Israel is one of the largest customers for US armaments.
It also receives several billion dollars a year in direct and indirect aid from Washington.