Oh Beirut, we want revenge against Lahoud and Bashar," they shouted.Syria condemned the assassination of Eido, saying it had nothing to do with the killing.
"Syria strongly denounces this crime and condemns the campaign of lies by some Lebanese used to accuse Syria after any killing and before an investigation even starts," a statement by the foreign ministry said.
Three ambulances carrying coffins of the victims were draped in Lebanese flags. Mourners carried white-and-blue flags of al-Hariri's Future Trend movement and filed past pictures of Eido and his son, a lawyer, with the slogan "Men of Justice".
Businesses, banks and schools were shut in Beirut and many other parts of Lebanon as the country observed a national day of mourning.
Eido and his son were due to be buried in Beirut after Muslim noon prayers.
Hariri's legacy
Eido belonged to the majority anti-Syrian parliamentary bloc of al-Hariri's son, Saad al-Hariri, that controls the government.
The bloc accused Syria of involvement in the attack and said it was in response to the establishment of a UN court to try suspects in political killings. A UN Security Council resolution setting up the tribunal went into effect on June 10.
The front-page headline of the daily al-Mustaqbal newspaper said: "Terrorism of Syrian regime challenges the court: Walid Eido martyred." The an-Nahar newspaper also described Eido as a martyr.
Hashem Ahelbarra, Al Jazeera's correspondent at the scene of the Beirut blast, said: "This is going to be a signal to the Lebanese that those who are carrying out the explosions are tracking people with real intelligence capability and manpower.
"Those who wanted to target [Eido] would have followed him from A to Z and when they saw him leave his car, they would have detonated the bomb.
'Clear pattern'
It was the sixth bomb in Beirut and the surrounding areas over the past four weeks. Two people were killed in the five previous explosions.
The bombs come as the Lebanese army has been locked in battle with Fatah al-Islam fighters in the northern Nahr al-Bared Palestinian refugee camp. At least 144 people have died in the continuing clashes.
Eido's death was likely to fuel tension between the government and the pro-Syrian opposition led by Hezbollah, a Shia Muslim group, which has condemned the killing.
The United States, France, Britain, the European Union and the United Nations joined in condemnations of the attack.
George Bush, the US president, said: "There has been a clear pattern of assassinations and attempted assassinations in Lebanon since October 2004.
"Those working for a sovereign and democratic Lebanon have always been the ones targeted. The United States will continue to stand up for Lebanon, its people, and its legitimate government as they face these attacks."
Fuad Siniora, Lebanon's prime minister, said the government was asking the UN commission investigating al-Hariri's assassination to help with the inquiry into Eido's killing.
Siniora also called on the Arab League to take action to protect Lebanon.
The UN Security Council, in a statement initiated by France, condemned "any attempt to destabilise Lebanon through political assassination or other terrorist acts".
Reduced majority
Rula Amin, Al Jazeera's correspondent in Beirut, said: "This was an assassination that did not take into account that it could kill civilians as well as those that it had targeted.
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