Protests have flared across the Muslim world against Israel's air strike on Qana, Lebanon, which killed at least 54 people - including many children.
Angry crowds filled streets and squares in countries including Iran, Iraq, Jordan and Syria.
There were many women among the crowds, some of whom referred to the images of dead children carried from the rubble.
Correspondents say crowds in several countries shouted pro-Hezbollah slogans and condemned Israel, the US and UN.
The BBC's Arab affairs analyst Magdi Abdelhadi, in the Egyptian capital Cairo, says the images from Qana will resonate throughout a region boiling with rage.
Support for Hezbollah
The right to demonstrate is severely restricted in many Arab countries, but thousands took to the streets on Monday.
In Iran about 1,000 people protested outside the UN office in Tehran.
They shouted support for Hezbollah leader Sheikh Hassan Nasrallah and burned US and Israeli flags.
There was anger as well as sombre protest
Children took part in the demonstration, displaying paintings of Israeli aircraft bombing Lebanese civilians and carrying banners calling for an end to the violence.
Shia Muslim women led protests in Baghdad's Sadr City neighbourhood, marching through the streets dressed in the traditional black Islamic chador.
Some carried coffins, while many flew the yellow flag of Hezbollah, or carried Lebanese flags.
"Today's demonstration is done by women and children only, because those murdered in Qana were women and children," Abu Mustafa, an organiser of the march, told the AFP news agency.
As well as rage against Israel for the killings at Qana, there was widespread anger at the US for what many saw as an act of complicity in allowing the conflict in Lebanon to continue.
In Syria, thousands gathered in the capital, Damascus, for a march organised by a women's union.
Protesters spoke of their anger at shock at the deaths in Qana, but also of a growing discontent with the international community and the UN.
The BBC's Jon Leyne in Damascus says the attack has unified Arabs about Hezbollah, even Sunni and Christian Arabs.
Some protesters turned their anger on Arab governments, accusing their leaders of failing to stand up to Israel's military strength.
In the Jordanian capital Amman reports said up to 1,000 people gathered at one of the city's universities.
"This is a cry against Arab and international complicity and silence over the massacres," Razan Zuaytar told the Jordan Times newspaper.
"This is a cry for governments, whose silence is the same as taking part in these crimes."
There were also reports of smaller protests in Kuwait, Indonesia and India.
[Note: The number of people killed in the Israeli bombing of Qana was later revised. The Washington based human rights group Human Rights Watch investigated the incident and issued a report on 3 August saying that 28 people were known to have died, while 13 people were missing.]