U.S. Secretary of State John Kerry was overheard on Sunday expressing what appeared to be pointed concern over the deaths of civilians during an Israeli offensive in Gaza.

In a conversation caught on an open microphone before an interview, Kerry made what seemed to be a sarcastic remark about Israel's insistence it was doing its utmost to avoid civilian casualties in operations against Hamas militants.

"It's a hell of a pinpoint operation. It's a hell of a pinpoint operation," he said during the call, which was broadcast on "Fox News Sunday."

While Washington says Israel has a right to defend itself from rocket attacks launched out of Gaza, American diplomats have called on the Israelis to restrict themselves to a precise operation in the ground campaign launched on Thursday.

On Sunday, more than 60 Palestinians, including women and children, were killed as Israel shelled a Gaza neighborhood and battled fighters. Thirteen Israeli soldiers also were killed. Kerry was expected to travel to the Middle East soon to press for a ceasefire.

"We got to get over there," Kerry said in his overheard comments, apparently to an aide. "I think, John, we ought to go tonight. I think it's crazy to be sitting around."

When Kerry was asked to explain the comments, he did not criticize Israel and emphasized its right to defend itself.

"I reacted obviously in a way that, you know, anybody does with respect to young children and civilians. But war is tough," he said.

Israel, which has accused Palestinian militant group Hamas of using civilians as human shields by launching rockets from residential areas, sent ground forces into the Gaza Strip after 10 days of air, naval and artillery barrages.