(CNN) -- Anti-government protests across Syria -- one propelled by the funeral of an assassinated Kurdish opposition leader -- turned deadly again Saturday as security forces cracked down, activist groups said.
Mashaal Tammo, a spokesman for the Kurdish Future Party and a member of the newly formed Syria National Council, was shot dead Friday at a private residence in the northeastern city of Qamishli.
The London-based Syrian Observatory for Human Rights said after Tammo's funeral, more than 50,000 people joined a mass demonstration demanding the overthrow of the government of Bashar al-Assad. It said two people were killed.
The group said a 14-year-old child was killed in Damascus province and 14 others were injured when security forces opened fire on a funeral procession for protesters killed Friday.
The Local Coordination Committees (LCC) of Syria reported a different toll. It said five people were killed in Qamishili. Another two died in Hama; one in Douma; and one in the Damascus suburb of Dumair.
Meanwhile in London Saturday, five protesters were arrested outside the Syrian Embassy.
A spokesman for London's Metropolitan Police said three people were arrested after climbing the roof of the embassy and two others were taken into custody for separate incidents related to the protest. There was no breach of security, the spokesman said.
In Qamishili, anti-government activists were also staging a general strike to mourn Tammo, the LCC said.
The state-run Syrian Arab News Agency (SANA) reported Friday that he was killed by "an armed terrorist group." Local activists said he was slain by members of a pro-government militia.
Catherine Ashton, the European Union's foreign affairs chief, condemned the assassination "in the strongest terms," in a statement Saturday.
"Mr. Tammo's death follows other targeted assassinations in the past days, which are totally unacceptable. These appalling crimes further add to the EU's grave concern over the situation in Syria. All those responsible for and complicit in these crimes must be held accountable," the statement said.
Tammo had previously spent more than three years as a political prisoner for his criticism of the Syrian government, it added.
In Istanbul, Turkey, several dozen Syrians gathered in a hotel basement to remember Tammo.
"The regime is trying to play a game of ethnicity so people fight each other," said Omar Shawaf, a Syrian opposition activist. "Mashaal Tammo was someone who represented unity of ethnic groups. This dirty regime will not keep quiet until they destroy the country and create a civil war."
Mourners relied on some of the same technology that has publicized the uprising in Syria, a country where the media is strictly controlled..
"The government tried to kill him one day before his murder and one month before his murder," said Abdul Ghafar Mohammed, speaking via Skype from Qamishli. "Now Tammo has become a flame of the revolution."
In Arabic, Tammo's first name, Mashaal, means flame.
The EU's Ashton also condemned the beating of opposition leader Riad Saif and urged an end to all violence to allow for a peaceful transition to democracy.
A White House statement Friday said Saif was subjected to a "vicious and unprovoked assault."
The LCC described the attack on Saif, who was beaten in the Damascus neighborhood of Medan, as a "dangerous development" and said the Syrian government was taking advantage of the "lax attitude" of the international community to repress political opponents by violent means.
The Syrian Observatory said Saturday that tens of military tanks were blocking routes out of the western city of Homs, a day after protests over the death of Tammo were held there. Mobile and landline networks were reported to be down.
Clashes also broke out Saturday between security forces and protesters who had pulled down a statue of al-Assad, the LCC said.
The United States called Friday for al-Assad to "step down now" following the assassination and amid continuing violence in the nation.
Assad should resign "before taking his country farther down this very dangerous path," White House spokesman Jay Carney said in the White House statement.
"It is also notable that these acts of violence took place just three days after the U.N. Security Council failed to pass a resolution calling for international human rights monitors in Syria in face of brutal repression," he said, referring to a resolution vetoed by Russia and China.
Earlier this week, Russia and China vetoed a U.N. Security Council draft resolution condemning Syrian authorities for using violence against anti-government demonstrators.
The two nations argued the proposed resolution would lead to military intervention similar to the NATO operation to protect anti-government protesters in Libya.
CNN's Ivan Watson and Salma Abdelaziz contributed to this report.