Israel has yet to make a decision whether or not to strike Iran's nuclear facilities, U.S. Defense Secretary Leon Panetta said Tuesday - as the American chief of staff estimated that Israel would not be able to destroy Tehran's nuclear program by itself.

Speaking during a press briefing, Panetta said: "Obviously Israel has to respond to that question. But from our point of view, the window is still open to try to work towards a diplomatic solution."

"I don't believe they made a decision as to whether or not they will go in and attack Iran at this time," Panetta said. "Obviously, they're a sovereign country. They'll ultimately make decisions based on what they think is in their national security interest. But I don't believe they made that decision at this time."

Panetta added that America still thinks there is room to negotiate. "The additional sanctions have been put in place. They're beginning to have an additional impact on top of the other sanctions that have been placed there," he said.

"The international community is strongly unified in opposition to Iran developing any kind of nuclear weapon. And we are working together, both on the diplomatic side as well as on the economic side, to apply sanctions. I said and I'll continue to repeat - the prime minister of Israel said the same thing - that any kind of military action ought to be the last alternative, not the first," he added.

General Martin Dempsey, the chairman of the Joint Chiefs of Staff, who was also present at the briefing, said that militarily, his assessment hasn't changed. "And I want to make clear, I'm not privy to their planning," he said.

"So what I'm telling you is based on what I know of their capabilities. And I may not know about all of their capabilities. But I think that it's a fair characterization to say that they could delay but not destroy Iran's nuclear capabilities," Dempsey said.

Panetta also stated that he spoke on Tuesday with his new Egyptian counterpart General Abdel-Fattah El-Sisi and had "a very good conversation" with him.

"He is a highly experienced officer who was trained and spent a lot of time in the United States. General el-Sissi expressed his unwavering commitment to the U.S.- Egypt mil-to-mil relationship, which has been really an anchor of stability in the Middle East for more than 30 years."

The U.S. defense secretary said that "el-Sissi has stressed that he takes seriously Egypt's obligations under the Camp David treaty, and he's committed to preventing the Sinai from becoming a staging area for militants. I indicated that I look forward to working closely with him to advance our shared goals in the region."