"Expected" and "worrisome" were among the words used by senior Israeli officials on Sunday to describe the outcome of the historic presidential elections in Egypt which saw the Muslim Brotherhood's candidate, Mohamed Morsi, crowned the largest Arab nation's newest leader.

Several officials said Morsi's victory marked a "new reality" in the Middle East and that Israel must prepare for Egyptian demands to reopen and insert changes into the peace treaty, changes that could include the deployment of additional Egyptian troops in Sinai.

Israel's peace agreement with Egypt, its first with an Arab country, is a cornerstone of Israeli security. The agreement ended decades of hostilities, with five wars and thousands of deaths on both sides.

While relations have never been warm, Egypt has upheld the deal, keeping its bordering Sinai Peninsula largely demilitarized, allowing the Israeli military to focus on other hostile borders with the Palestinians, Syria and Lebanon.

One official source, commenting Sunday on Morsi's win, said: "There were some in the West who laughed at us when we said the Arab Spring would turn into an Islamic Winter. Now it is clear who replaced Mubarak. The Muslim Brotherhood will either become more involved in the political process and less extreme, or vice versa — they will transform Egypt into a much more extreme state with their hold over the parliament and presidency."

The Prime Minister's Office released a short and restrained statement on Morsi's victory, saying, "Israel appreciates the democratic process in Egypt and respects the results of the presidential elections. Israel looks forward to continuing cooperation with the Egyptian government on the basis of the peace treaty between the two countries, which is a joint interest of both peoples and contributes to regional stability."

Officials in Israel hope that with the Muslim Brotherhood's rise to power, the central government in Cairo will seek to demonstrate governance and sovereignty over the increasingly anarchic Sinai and prevent terror attacks from coming out of the peninsula.

However, the political echelon in Israel is still concerned with two questions regarding the new political reality in Egypt: To what extent will the Muslim Brotherhood continue military cooperation with Israel; and how will the relationship between the brotherhood and its sister organization, Hamas, in Gaza, play out?

Intelligence and Atomic Energy Minister Dan Meridor, speaking Monday at the Jewish Agency Board of Governors meeting in Jerusalem, said that the question of democracy in Egypt was now going to be tested by how the Muslim Brotherhood treats the issues of human rights.

"The neighborhood we live in is unstable; the world around us is shaking, trembling. A year and a half ago, when the whole thing started in Cairo in Tahrir Square, as minister of intelligence, I had no clue that it was going to happen. The whole Arab awakening took us by complete surprise, as it took Mubarak and his people by surprise. On Egypt, we look very closely and attentively to what they say and do. There was an election; we of course respect the election and the result. There is no reason that cooperation shouldn’t continue. The slogans in Cairo were about freedoms, representation and human rights, not 'kill the Jews.' The revolution was not started by army officers or political parties but by average people. The people wanted democracy. There is a majority government there now, and there is now a test of democracy. Does the majority always want democracy? What if the majority doesn’t want women's right, for instance? What about human rights? We see the awakening of political Islam all over the world, from Afghanistan to northern Africa. We hope that it ends up with democracy and more freedom. We have a keen interest that the Begin-Sadat agreement continues because this was the cornerstone not only for peace but of stability all over the region."

Labor MK Binyamin (Fouad) Ben-Eliezer, a former defense minister who maintained close ties with deposed Egyptian President Hosni Mubarak, also commented on Morsi's victory, saying, "[The Mubarak] era is over and done with. We are witnessing only the beginning of the revolution now, not the end of it. While Israel should establish channels of dialogue with the Islamists, it must also prepare for a future conflict with Egypt."

With the Egyptian military still the ultimate power in Egypt, senior Israeli defense officials who maintain contacts with Egypt said Sunday that they do not expect any immediate changes in relations. Over the long term, they warned, the Brotherhood may seek to cancel the peace agreement. The officials spoke on condition of anonymity because they were discussing a sensitive security assessment.

Eli Shaked, a former Israeli ambassador to Egypt, said the Egyptians would "have a lot to lose" if they canceled the peace, including Western investment and billions of dollars in U.S. aid. Even so, he warned, the treaty was not safe.

Meanwhile, the White House on Sunday congratulated Morsi and urged him to advance national unity as he forms a new government.

White House press secretary Jay Carney said Morsi's victory is a milestone in Egypt's transition to democracy after decades of authoritarian rule under Mubarak. The Obama administration had expressed no public preference in the presidential race.

U.S. President Barack Obama on Sunday called Morsi to congratulate him on his victory and offer continued U.S. support for Egypt’s transition to democracy.

Obama “emphasized his interest in working together with President-elect Morsi, on the basis of mutual respect, to advance the many shared interests between Egypt and the United States,” the White House said.

“Morsi expressed appreciation for Obama’s call and welcomed U.S. support for Egypt’s transition,” the White House said in a press release. Obama and Morsi also agreed to stay in close touch in the coming weeks and months.

The Muslim Brotherhood’s victory adds a new element of uncertainty for U.S. policy in the Middle East, which has been rocked by the conflict in Syria, where some 40 people were said to have died Sunday in new clashes between rebels and government forces.

The U.S. provides about $1.3 billion annually in military aid to Egypt; the two countries regularly hold joint military exercises, and U.S. Navy ships are frequent visitors to Egyptian ports.

Iran on Sunday also congratulated Morsi on his victory, saying Egypt was in the final stages of an "Islamic awakening."