Updated

From Mideast countries to European capitals, protesters took to the streets Monday to condemn Israel's assault on Gaza that has so far left at least 315 people dead, wounded hundreds more and reduced dozens of buildings to rubble.

By far the largest protest in the Arab world — where outrage over Israel's air strikes continued into a third day — took place in Lebanon, with tens of thousands of Lebanese Hezbollah supporters standing under pouring rain.

The protesters thronged a huge square and nearby streets in the militant group's stronghold south of Beirut, carrying Palestinian, Lebanese and yellow Hezbollah flags and banners supporting the Palestinian people.

• Click here to see photos of the international protests.

The massive rally was called for by Hezbollah leader Hassan Nasrallah who in a speech on Sunday urged crowds in the Arab and Islamic world to rise up in support of Gaza and declared Monday a day of mourning and solidarity with Gaza.

Addressing the crowds on Monday through a large screen from an unknown location, Nasrallah urged Palestinians to unite and sought to boost morale.

"Israel's air force will fail to destroy the will of the (Palestinian) fighters firing rockets ... and the residents of (Israeli) settlements 20 and 40 kilometers away from Gaza will remain either outside their settlements or in shelters," he said.

"Death to Israel," and "At your service, Gaza!" many in the crowd shouted.

Nasrallah warned Israel that any ground offensive will result in many losses for the Israelis and said Israel will fail as it did when it fought Hezbollah guerrillas in a monthlong air and ground offensive in 2006.

The overwhelming Israeli bombing campaign, the deadliest against Palestinians in decades, had killed 315 people by Monday morning.

In the southern Lebanese port city of Sidon, around 3,000 people also staged a demonstration, many of them chanting slogans in which they insulted the rulers of Egypt, Jordan and Saudi Arabia for perceived complicity with Israel.

In Egypt, which has been particularly criticized for joining Israel in closing its borders with Gaza, thousands of people rallied, calling for the active intervention of Arab armies to protect the Palestinians.

Demonstrations were held near the parliament building and in downtown Cairo amid a massive security presence of black-clad riot police. Demonstrations in the tourist destination of Luxor, however, were prevented.

The largest protest, a crowd of up to 3,000 people outside the Journalists' Union, was organized by the opposition Muslim Brotherhood, and in an unusual move, the Islamist organization's Supreme Guide Mohammed Mahdi Akef took part, urging the crowd to make "their declaration of anger through peaceful means."

In Iran, a prominent conservative political party announced it is registering volunteers to fight against Israel in response to the attacks on Gaza.

The party, the Combatant Clergy Society, has provided three options for the volunteers on its Web site to fight Israel, including in the military, financial and propaganda fields — most signing up opted for the military option.

The group said Monday it decided to sign up volunteers after Iran's supreme leader, Ayatollah Ali Khamenei, issued a religious decree to world Muslims Sunday, saying anybody getting killed while defending Palestinians in Gaza would be considered a martyr.

In the Sudanese capital, Khartoum, thousands rallied for a second day over the Gaza attack. The protesters marched to the Egyptian embassy calling for an opening of the Egyptian-Gaza border for supplies and aid to the Palestinians. They also marched to the U.N. headquarters where they handed over a protest note.

In Iraq, about 1,000 backers of anti-American Shiite cleric Muqtada al-Sadr staged a protest in eastern Baghdad. "No, no to Israel," they shouted as they burned Israeli and American flags.

Separately, the political party of Iraqi Prime Minister Nouri al-Maliki issued a statement condemning the attacks and calling on Islamic countries to cut relations with Israel and end all "secret and public talks" with it.

Jordan's King Abdullah II donated blood to Gaza victims, telling reporters he was "upset" by the scale of the Israeli offensive in the coastal strip.

In Athens, a mixed group of some 300 Arab and Greek protesters threw rocks at the Israeli embassy and scuffled with riot police, in a demonstration organized by the Greek communist party. The Greek riot police fired stun grenades and volleys of tear gas to repel the protesters

Later, more than 3,000 demonstrators waving Palestinian flags and chanting anti-Israeli and anti-U.S. slogans converged on the Israeli Embassy north of the city center in separate demonstrations and rallies organized by Greek left-wing parties and Arab groups. In the northern Greek city of Thessaloniki, about 1,000 demonstrators protested outside the U.S. Consulate, where they burned an Israeli flag.

There were also protests Monday in Berlin, where about 2,000 marched through a central shopping district carrying Palestinian flags and banners saying Israel must end the Gaza blockade, and in London, where around 600 protested outside the Israeli embassy. Both rallies passed peacefully.