Behind an official wall of silence, Israel watched nervously Saturday as anti-government unrest worsened in Egypt, fearful that the violent and growing street protests could topple Israel's most important ally in the Arab world.

Prime Minister Benjamin Netanyahu ordered his government to remain silent about the situation in Egypt. But in a clear reflection of Israel's concerns, Sun D'Or, a subsidiary of Israel's national airline, El Al, whisked dozens of Israelis, including diplomats' families, out of Egypt on an emergency flight. The government also urged Israelis to avoid travel to Egypt.

The stability of Egyptian President Hosni Mubarak's regime is a key interest for Israel.

Egypt was the first Arab country to make peace with Israel, and since succeeding the assassinated Anwar Sadat in the wake of that historic peace treaty three decades ago, Mubarak has steadfastly honored the deal.

While relations have often been cool, Mubarak has remained a key bridge to the Arab world, frequently mediating between Israel and the Palestinians. Mubarak also has cooperated with Israel in containing the militant Hamas group, which rules the Gaza Strip, a volatile coastal strip that borders both Israel and Egypt.

Israeli officials, ordered to speak on condition of anonymity, expressed grave concerns about Mubarak's tenuous grip on power. Some said they feared the violence could spread to neighboring Jordan, the only other Arab country with a peace deal with Israel, or to the Palestinian territories.

There were also concerns that anti-Israel opposition groups, including the fundamentalist Muslim Brotherhood, might gain a larger voice in Egyptian decision-making.

"A stable Egypt with a peace treaty with Israel means a quiet border," one Israeli official told The Associated Press. "If there is a regime change Israel will have to reassess its strategy to protect its border from one of the most modern militaries in the region."

Early Saturday evening, the Sun D'Or International Airlines plane touched down in Israel with about 40 Israelis who were in Egypt on private business plus an undisclosed number of diplomats' spouses and children on board, officials said. The Israeli Foreign Ministry said its diplomats would remain in Egypt for the time being.

The Egyptian unrest dominated Israeli media. Israeli TV news channels provided nonstop updates throughout the day. State-funded Israel Radio reported extensively on developments and dubbed its broadcasts "Fire on the Nile."

Writing in the Haaretz daily Saturday, columnist Aluf Benn speculated that Mubarak's "fading power" leaves Israel with few friends in the Middle East.

Mubarak has faced days of massive anti-government protests, with tens of thousands of people filling the streets of Cairo and other major cities demanding his resignation after nearly 30 years in power. The protesters have said they are fed up with the massive unemployment, lack of opportunities and corruption that plague the country.

On Saturday, Mubarak named Omar Suleiman, his powerful intelligence chief, as vice president, the first time someone has held that position since he became president in 1981. It was unclear whether the move, which followed promises of reform and a new government, would be enough to calm the unrest.

There was no immediate reaction from Israel, but the appointment was likely to calm nerves in Israel, where Suleiman is a frequent visitor and has good working relations with his Israeli counterparts.

Israeli officials said it was unclear if Mubarak would survive the protests, and they fear that ties could be damaged if Egypt's popular opposition group, the Muslim Brotherhood, makes gains.

Eli Shaked, a former Israeli Ambassador to Egypt, speculated in an interview with Channel 10 TV that if Mubarak's reign is destabilized, radical Egyptian Islamists could fill the void.

"It's good that Israel is keeping quiet, but there is no doubt that what is happening in Egypt is not good for Israeli interests," Shaked said. "It will only be a matter of time before a leader of the revolution arises and he will come from the Muslim Brotherhood.

A stronger Muslim Brotherhood could also affect the balance of power between the rival Palestinian camps, the government of President Mahmoud Abbas in the West Bank and the rival Hamas regime in Gaza.

Abbas is backed by the West, while his Islamic militant rivals draw their support from Iran, Syria and Hezbollah. Hamas is the Gaza branch of the Muslim brotherhood and could gain strength if their Egyptian brethren rise to power.

Abbas on Saturday called Mubarak, according to the Palestinian news agency Wafa. Abbas told the Egyptian leader that he is eager to see Egypt stable and secure, the agency said.

There was no immediate comment from Hamas.

In Gaza, Palestinian residents rushed to buy extra gasoline, concerned that fuel supplies would run out. In the past few years, the majority of Gaza's fuel has come from Egypt through underground smuggling tunnels on the Gaza-Egypt border.

Palestinian smugglers who work in the tunnels said Saturday that there were fewer fuel supplies available from Egypt, but that they were continuing to smuggle Egyptian fuel into Gaza. The Hamas-run National Economic Ministry, which oversees fuel supplies, said there were currently no fuel shortages in Gaza.

Hamas Interior Ministry spokesman Ihab Ghussein said there were no infiltrations on the Gaza-Egypt border.

"The southern border with the Gaza Strip is quiet. There is no security breach on that border," Ghussein said.

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Ibrahim Barzak in Gaza City, Gaza Strip, contributed to this report.