Several of Sunday's protests turned violent. A crowd of anti-Israel protesters in the northern Iraqi city of Mosul became a target for a suicide bomber on a bicycle.
In Lebanon, police fired tear gas to stop dozens of demonstrators from reaching the Egyptian Embassy. Some in the crowd hurled stones at the embassy compound. It was unclear if anyone was hurt.
Egypt, which has served as a mediator between Israel and the Palestinians as well as between Hamas and its rival Fatah, has been criticized for joining Israel in closing its borders with Gaza.
Egyptian Foreign Minister Ahmed Aboul Gheit called on Hamas to renew its truce with Israel: "There has been a calm and we should work to restore it."
France also called for the truce to be renewed and rallied European nations to use "all their weight" to stop the fighting between Israel and Hamas.
"We have entered a new spiral of despair," French Foreign Minister Bernard Kouchner told the Journal du Dimanche in an interview published Sunday. "The truce must be restored."
Kouchner noted that the attacks come "in a context of vacancy of power in Israel and the U.S." as both countries are undergoing leadership transitions.
"Europe has a role to play," Kouchner said.
In Beirut, Hamas representative Osama Hamdan told the crowd that the militant group had no choice but to fight. Gaza militants have been lobbing dozens of rockets and mortars into southern Israel since a six-month truce expired over a week ago, prompting Israel's fierce retaliation.
"We have one alternative which is to be steadfast and resist and then we will be victorious," Hamdan said.
In the capital of neighboring Syria, more than 5,000 people marched toward the central Youssef al-Azmeh square, where they burned an Israeli and an American flag.
One demonstrator carried a banner reading, "The aggression against Gaza is an aggression against the whole Arab nation."
"Down with America, the mother of terrorism," read another.
In Amman, Jordan, about 5,000 lawyers marched toward parliament to demand the Israeli ambassador's expulsion and the closure of the embassy. "No for peace, yes to the rifle," they chanted.
In Jordan's squalid Baqaa camp for Palestinian refugees and their descendants, protester Yassin Abu Taha, 32, blamed America and Israel for the Middle East's problems.
"The Israelis kill our people in Gaza and the West Bank. The Americans kill our people in Iraq. We're refugees, kicked out of our home in Tulkarem in 1967 and we're still displaced," he said, bemoaning his family's flight in the 1967 Mideast war.
The U.S. Embassy in Jordan warned Americans to avoid areas of demonstrations.
Thousands of Egyptians - many of them students - demonstrated at campuses in Cairo, Alexandria and elsewhere and accused President Hosni Mubarak and other Arab leaders of not doing enough to support the Palestinians.
Iran's president, Mahmoud Ahmadinejad, who has said Israel should be "wiped off the map," denounced the Israeli strikes.
And in the normally politically placid streets of glitzy Dubai, hundreds of demonstrators - some draped in Palestinian flags - gathered at the Palestinian consulate.
"This is a time for the Palestinians and Arabs to unite to fight against a common enemy," said Majdei Mansour, a 30-year-old Palestinian resident of Dubai. Mansour said he has been unable to contact his family in Gaza since the latest fighting.
In Iraq, where the government has also condemned the Gaza airstrikes, a suicide bomber on a bicycle blew himself up amid a crowd of about 1,300 demonstrators in Mosul who were protesting against Israel, killing one demonstrator and wounding 16, Iraqi police said.
There was no claim of responsibility for the attack on the demonstration, which was organized by a Sunni party in sympathy for Palestinians in Gaza, who are largely fellow Sunnis.