U.S. Secretary of State John Kerry responded Wednesday to Israeli Defense Minister Moshe Ya'alon's attack, saying he did not intend to let "one set of comments undermine peace efforts."

"I will work undeterred," Kerry told reporters at a press conference in Kuwait, a day after Ya'alon set off a diplomatic incident for calling him "obsessive and messianic". The secretary of state did not mention Ya'alon's apology during his briefing, specifying only that he wanted to see progress in peace efforts.

"After 5 months of negotiations, I believe strongly in the prospects for peace and I know the status quo is not sustainable," said Kerry. "We've always known that as we approach the time for these difficult choices, it's going to be difficult."

Ya'alon apologized just before midnight Tuesday for "insulting" the secretary of state.

"The defense minister did not intend to insult the secretary and he apologizes if the secretary was hurt by the remarks attributed to the defense minister," read a statement issued by Ya'alon's bureau.

The apology was issued after two-hour meeting between Ya'alon and Prime Minister Benjamin Netanyahu at the premier's residence in Jerusalem. The statement, which was composed together with Netanyahu, followed a lukewarm response from Ya'alon earlier in the day which was rejected by the Obama Administration.

Senior American officials said prior to Ya'alon's apology that the United States was not satisfied with the Israeli government's response to the remarks and expected Netanyahu to issue a public condemnation.

"We expect the Prime Minister to put this right by publicly expressing his disagreement with the statements against Secretary Kerry, the negotiations with the Palestinians and Kerry's commitment to Israel's security," said a senior U.S. official.

Ya'alon's statements sparked serious tension between the two countries over the course of the day. State Department Spokeswoman Jennifer Psaki told Haaretz on Tuesday evening that Ya'alon's remarks, if accurate, were "offensive and inappropriate, especially given all that the U.S. is doing to support Israel's security needs."