French TV reporter Gilles Jacquier has been killed in the Syrian city of Homs, the first Western journalist to die in the country's current unrest.
He was on a government-authorised trip to the city, the France 2 channel said.
Syrian TV said Jacquier was among eight killed. A colleague said that minutes earlier they had interviewed some people at a pro-government gathering.
Opposition groups say 24 people died around the country on Wednesday, including 10 in Homs.
French Foreign Minister Alain Juppe has called for full clarification of what happened.
"We vigorously condemn this odious act," he said in a statement.
EU foreign policy chief Catherine Ashton said an investigation was needed.
"The Syrian authorities have a responsibility to guarantee the safety of journalists in their country," she said.
More than 5,000 people have been killed since the unrest began last March, the UN says. The government says 2,000 security personnel have died combating "armed gangs and terrorists".
It is impossible to verify the claims as access for foreign journalists has been severely restricted.
Observers arrived in Syria in December to monitor an Arab League peace plan, but the killing has continued.
The league said on Wednesday it was delaying sending more monitors after an attack on an observer team earlier in the week, Reuters news agency reported.
Eleven observers were slightly injured in the attack, in the port city of Latakia.
Meanwhile at a joint news conference US Secretary of State Hillary Clinton and Prime Minister Sheikh Hamad bin Jassim al-Thani of Qatar, a key member of the Arab League, expressed doubts about the mission.
"I could not see up until now a successful mission, frankly speaking," Mr al-Thani said.
Jacquier, 43, was part of a group of 15 foreign journalists being shown around a part of Homs and speaking to locals.
One of his colleagues said they were escorted by soldiers and police, and were in a part of the flashpoint city where street life was relatively normal with some shops open.
A grenade fell close to them minutes after they had spoken to some young people and they fled into a nearby building, he told the BBC. More grenades hit the building causing casualties.
"There was smoke everywhere, people started screaming and yelling. There was complete chaos," he said.
Jacquier was behind him when he went into the building, but he saw him lying dead a few minutes later, he added.
At least one other European journalist was wounded, reports say. Dutch officials and media said a Dutch journalist was hurt.
The area of the attack is inhabited by members of the Alawite sect and therefore considered to be mainly pro-government. No opposition supporters have given an account of the incident.
Jacquier is described as a veteran award-winning journalist who covered conflicts in Iraq, Afghanistan and Kosovo, and between Israel and the Palestinians.
His mission in Syria was to make a documentary film on the protests.
The UN Security Council has been told that an estimated 400 people had been killed in Syria since the Arab League monitors arrived in late December - an average of almost 40 deaths a day.
Opposition group the Local Co-ordination Committees said 24 people died in violence on Wednesday - 10 in Homs, nine in Hama, two each in Aleppo and Idlib and one in Latakia.
The security situation led the US state department to announce it had further reduced numbers of staff at its embassy in Damascus, after ordering family members to leave in October.
Meanwhile, President Bashar al-Assad made a surprise appearance at an open air rally by thousands of his supporters in Damascus.
Mr Assad said he wanted to show his love for the Syrian people.
His wife, Asmaa, and his children were also briefly shown in the live broadcast. There had been speculation that they might have have left Syria.