After four days of Israeli airstrikes on Gaza, an outpouring of popular anger is putting pressure on American allies in the Arab world and appears to be worsening divisions in the region.

The sharpest rhetorical attacks have been aimed at Egypt, which is widely seen as having aided the Israeli campaign by closing its border with Gaza.

But as major street demonstrations continued Tuesday from North Africa to Yemen, some marchers and opinion-makers also lashed out at other moderate Arab governments for failing to take a stronger stand. Syria and Iran, meanwhile, have drawn praise for their militancy.

The Egyptian president, Hosni Mubarak, gave a televised address to defend his decision not to open the border with Gaza except for humanitarian purposes. He derided “those who are seeking political gains at the expense of the Palestinian people.”

Although Jordan and Saudi Arabia — solid American allies — have been careful not to blame Hamas publicly, the violence has put them on the defensive, too.

“It’s becoming clear that if you are silent, the Arab street is going to consider you part of the enemy,” said Muhammad al-Masri, a researcher and political analyst at the Center for Strategic Studies in Amman, Jordan. “There is no way to be in the middle.”

The polarization appears to have ended a thaw that had taken place in the past year, Mr. Masri said. Syria had been reaching out to the West and holding indirect peace talks with Israel. Lebanon’s political factions had reached a peace deal. Syria and Saudi Arabia had made gestures toward resolving their feud.

Now, fault lines visible during the summer 2006 war between Israel and Hezbollah have reappeared. Syria has been pressing for an emergency Arab summit meeting, but Egypt and Saudi Arabia have resisted.

Although the conflict has sectarian overtones — many Sunni Arabs fear that Iran wants to extend its Shiite influence — it is rooted in politics, not religion.

To some extent, the outrage has forged a sense of trans-sectarian unity, allowing militant Shiite figures like Hassan Nasrallah, the leader of Hezbollah, to extend his influence in the Sunni Arab world, as he did during the 2006 war.

Demonstrations continued Tuesday in Cairo, where marchers have been carrying banners for days with slogans like “Down with Mubarak” and “Where is the Egyptian Army?” Angry disputes have broken out in the Egyptian Parliament, with members of the Muslim Brotherhood — the ideological parent of Hamas — accusing the government of colluding with Israel.

Protesters attacked the Egyptian Consulate in Aden, Yemen, on Tuesday, and 11 were arrested. There have been similar assaults on symbols of Egyptian authority in the region since Sunday.

In Tehran, a group of 30 to 40 students broke into the British Embassy’s residential compound, where they vandalized buildings and replaced the British flag with a Palestinian flag, according to a witness and an embassy official.

Egypt is trapped between Israel, with which it has a peace treaty, and Hamas, which has popular support among Egyptians. The government has struggled with its own Islamist opposition and does not want Hamas operatives to cross into its territory, but it faces popular anger if it appears to endorse violence against Palestinians.

The Israeli airstrikes that began Saturday have exacerbated the situation. Hamas is ruling Gaza and is politically isolated from the West Bank, putting the onus more than ever on Egypt, the only state besides Israel that borders Gaza.

“Egypt is very much cornered this time,” said Hassan Nafaa, a professor of political science at Cairo University. “There’s a perception that Egypt is leading the moderate Arab camp in this, and that the moderate camp has not been able to achieve anything.”

Egyptian officials see the hand of Iran, a patron of Hamas, in the current conflict. Iran had been pressing Egypt before the conflict, apparently eager to undermine Egypt’s role as a mediator between the Palestinian factions. Demonstrators gathered in front of the Egyptian Embassy in Tehran on Dec. 17 to protest Egypt’s position toward Hamas.

Recently, government-allied newspapers in Egypt have lashed out at Iran and its ally Hezbollah, whose leader, Hassan Nasrallah, demanded Sunday that Egypt open its border and allow weapons and supplies to flow to Hamas.

Mr. Nasrallah “has illusions that people in Egypt will take his orders, and that the government here submits to the kind of bribery he is used to in his country,” wrote Usama Saraya in Tuesday’s edition of Al Ahram, an Egyptian daily newspaper.

Television stations and newspapers allied with Iran and Syria continued to portray Egypt as a traitor. Some commentators had harsh words for other Arab states.

Saudi Arabia and Egypt “are even more excited about this war than they were during the 2006 war” between Israel and Hezbollah, said Ibrahim al-Amine, the chairman of the board of Al Akhbar, a newspaper aligned with Hezbollah.

“Israel would be satisfied with a compromise, but the Arab regimes want to finish Hamas completely,” Mr. Amine said.

They cannot openly say so, he added, because Hamas is a Sunni movement, unlike Hezbollah, which Saudi Arabia and Egypt — both of them Sunni-led countries — publicly criticized at the start of the summer 2006 war with Israel.