In a rare comment on the internal politics of a US ally, State Department spokesman Mark Toner said Washington had "seen reports from Israel describing it as the most right-wing coalition in Israel's history."
"And we also know that many of its ministers have said they oppose a two-state solution. This raises legitimate questions about the direction it may be headed in and what kind of policies it may adopt."
Earlier, Israeli Prime Minister Benjamin Netanyahu had named hardline nationalist Avigdor Lieberman as defense minister and welcomed lawmakers from his Yisrael Beitenu party to the ranks of his coalition.
Netanyahu has continued to insist that he wants to negotiate peace with the Palestinians, but Lieberman's arrival in the cabinet has raised concerns inside and outside of Israel that it will toughen its stance.
"Ultimately we're going to judge this government based on its actions," Toner said.