US Secretary of State John Kerry has appeared to criticise Israel's Gaza operation in a "hot mic" moment between interviews with Fox News.

"Fox News Sunday" host Chris Wallace confronts Kerry - around the 10:30 mark in the video above - with footage of him sarcastically calling the Israeli operation "pinpoint".

"It's a hell of a pinpoint operation. It's a hell of a pinpoint operation," he says to the aide named only as John.

"We've got to get over there. Thank you John. I think John we ought to go tonight. I think it's crazy to be sitting around," he continues.

Kerry is asked to clarify his comments by the host and, in the awkward exchange, Kerry says that he was alluding to the difficulty that Israel faces when trying to achieve their aims in such a dense area.

"You have people who come out of tunnels. You have a right to go in and take out those tunnels.

"We completely support that and we support Israeli's right to defend itself against rockets that are continuing to come in.

"Hamas has started this process of rocketing after Israeli was trying to find the people who killed... three young Israeli citizens. It's disgraceful. So yeah, it's tough. It's tough to have this kind of operation," he concluded.

The comments come after 62 Palestinians were killed by Israeli shelling of the Gaza neighbourhood of Shejaiya and 13 IDF soldiers were killed in firefights.

The Director of Shifa hospital, Naser Tattar, said that 17 children, 14 women and four elderly civilians were among the 50 people killed while 400 more were wounded. Thousands were evacuated to UN shelters in the centre of Gaza City.

425 Palestinians have now been killed in the operation with almost 3000 wounded, according to the Gaza Health Ministry, while 20 Israelis - 18 troops - have been killed in fighting with Palestinian militants.