The Israeli government has spied on U.S. Secretary of State John Kerry's peace negotiations in the Middle East last year, according to German magazine Der Spiegel.

The magazine said on Sunday that an Israeli intelligence agency and at least one other agency had intercepted Kerry's phone calls with high-ranking officials from Palestine and other Arab nations. It claimed that the calls were made over unencrypted and unsecure lines.

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The conversations, which were intended to negotiate a peace deal in the region, had been used by the Israeli government in hopes of reaching "a diplomatic solution in the Middle East," the publication said.

So far, neither Jerusalem nor Washington has commented on the matter.

After talks of a truce that failed last year, relations between Israel and the U.S. have been strained.

Last week, Washington hit back against Israel's "misinformed" criticism of Kerry's negotiations for a ceasefire in the region.

Jerusalem had accused Kerry of favoring the Hamas for his attempts to include Qatar and Turkey into the negotiations. It also slammed the envoy for dismissing some of their key concerns in the conflict including the destruction of the Hamas' tunnels and the demilitarization of Gaza.

Israeli Defense Minister Moshe Ya'alon said Kerry was messianic and obsessive, and indirectly called for the latter's withdrawal in the cease-fire negotiations.

Earlier this month, Kerry also earned Israeli ire after he warned Israel of becoming an "apartheid state," which Israeli Intelligence Minister Yuval Steinitz described as being "offensive, unfair and insufferable."

On Sunday, Israel's missile attack of a humanitarian school in the Gaza strip was criticized by the U.S.

Jen Psaki, spokeswoman for the U.S. State Department, said the U.S. was appalled by the attack and reiterated that Israel needs to "do more to meet its own standards" and prevent civilian casualties.

Still, it seems the U.S. is committed in providing support for Israel as Congress voted on Friday for a US$225 million funding of the Iron Dome system, which is intended to restock Israel's missile defenses.

TagsIsrael, Hamas, wiretapping, John Kerry, Moshe Ya'alon, Yuval Steinitz, Benjamin Netanyahu, Gaza, school bombing, Jen Psaki, failed peace talks, cease fire