Key Arab allies of the United States, predominantly Sunni countries such as Saudi Arabia, Jordan and Egypt, fear the rising power of Shiites in the region: Hezbollah militants who virtually control southern Lebanon, Iraq's majority Shiite government, and — most worrisome — the Shiite theocracy that has run Iran for decades.
Yet many ordinary people, Sunnis as well as Shiites, are cheering the Lebanese guerrillas because of their willingness to stand up to Israel.
Sitting in the shade as he sold figs in downtown Cairo, Hasan Salem Hasan, a 25-year-old Sunni, summed up a prevailing attitude of the so-called Arab street: "Although Hezbollah is a Shiite party, we are all Muslims, and all Arabs will defiantly support them and fight the Jews."
On the one hand, predominantly Sunni Arab states are tacitly encouraging the destruction of Hezbollah, concerned it could stage attacks and create militant cells outside of Lebanon. There is also fear that militant Sunnis could join with Hezbollah — as the Palestinian militant group Hamas has done — to build a super terrorist network.
"Whenever there is a paramount cause which can bring them together, such as a jihad against the Zionists, they will be united," Gamal Sultan, editor of the Cairo-based Islamic monthly Al Mannar Al Jadid, said of the Sunni and Shiite militants.
Yet on the other hand, Arab governments also fear their own populations will turn on them if they look weak and unable to challenge Israeli aggression against a fellow Arab state.
Saudi Arabia — the bulwark of the Sunni Arab world — has tried to balance both concerns, criticizing Iran and Hezbollah for provoking Israel but also condemning the Jewish state. Israel started bombing south Lebanon, Hezbollah's base, after the guerrillas kidnapped two Israeli soldiers July 12.
The Saudi foreign minister, Saudi Al Faisal, on Tuesday blasted what he called "non-Arab intervention in the Arab world" — a clear reference to Iran, Hezbollah's main backer along with Syria.
Saudi media were even more outspoken.
"We are facing a fierce Iranian offensive against the region. We see that clearly in Iraq where Iran is becoming the major player and in Lebanon through its agent, Hezbollah," columnist Mishari Al Thaydi wrote in the Saudi-owned London-based Asharq Al Awsat newspaper.
Yet on Thursday, Saudi Crown Prince Sultan Bin Abdulaziz Al-Saud lashed out at Israel for its punishing airstrikes.
"We cannot tolerate Israel's playing with the lives of citizens, civilians, women, the elderly and children," he said after meeting with French President Jacques Chirac in Paris.
Other Sunni Arab leaders fear that growing Shiite power in Lebanon and Iraq will awaken Shiite minorities at home.
In April, Egyptian President Hosni Mubarak angered Shiite leaders by saying Shiites across the Middle East were more loyal to Iran than to their own countries.
Former Jordanian information minister Saleh al-Qalab has described Hezbollah as an Iranian "land mine" in the Arab world. And Jordan's King Abdullah II warned of a Shiite crescent forming in the region.
Some blame Washington's Middle East policies for upsetting the region's sectarian balance.
"The whole problem started with the American invasion of Iraq with the cooperation of Shiites," said Mamdouh Ismail, an Islamic activist and lawyer who defends Muslim militants in Egyptian courts. "This will certainly resonate throughout the whole region, in the Gulf ... in Saudi Arabia," he added.
Yet events in Lebanon have further mobilized the Shiites across the Muslim world and, if Hezbollah survives the current Israeli onslaught, the sect stands to become even stronger.
In Iraq, the Hezbollah-Israel conflict has proved a rallying point for Sunnis and Shiites otherwise riven by sectarian violence.
On Thursday, Iraqis staged an anti-Israel protest with banners reading "Shiites and Sunnis unite" in the city of Samarra, where the bombing of a Shiite shrine in February brought the country to the brink of civil war.
Earlier this week, about 4,000 Iraqis answered the call of Shiite clerics to rally in the holy city of Karbala in protest of Israeli attacks, raising Iraqi and Lebanese flags.
Iraqi Prime Minister Nouri al-Maliki — a Shiite — also condemned the Israeli destruction of Lebanon's infrastructure. "I call on the Arab League foreign ministers meeting in Cairo to take quick action to stop these aggressions. We call on the world to take quick stands to stop the Israeli aggression," he said.
On Tuesday, thousands of Shiites demonstrated in the Gulf kingdom of Bahrain in support of Hezbollah, two days after some 300 prominent Saudi Shiites wrote to the Bahraini government urging support to the Lebanese Shiite group.
Both moves were seen as an assertion of increasing Shiite solidarity across the Arab world.
Adding to the Shiite power base, the sect's faithful share a coherent religious view. Since splitting from their Sunni brethren in the 7th century over who should replace the Prophet Muhammad as Muslim ruler, they have developed distinct concepts of Islamic law and practices.
They also dominate by sheer number: Shiites account for some 160 million of the Islamic world's population of 1.3 billion people. Shiites account about 90 percent of Iran's population, more than 60 percent of Iraq's, and some 50 percent of the people living in the arc of territory from Lebanon to India.