U.S. Secretary of State Hillary Clinton said Wednesday that President Bashar al-Assad gave a "chillingly, cynical speech" in which he tried to shift the blame for the violence in Syria.

"Instead of taking responsibility, what we hear from President Assad in his chillingly cynical speech yesterday was only making excuses blaming foreign countries," Clinton said.

The United States on Wednesday denied that it was to blame for the killing of an Iranian nuclear scientist by a car bomb, after Tehran said Washington and Israel were responsible for the attack.

"The United States had absolutely nothing to do with this. We strongly condemn all acts of violence, including acts of violence like this," said National Security Council spokesman Tommy Vietor.

Syrian security forces killed 21 civilians and were clashing with army deserters in a town near the central city of Hama on Wednesday, activists and a human rights group said.

Twenty-one civilians and three army deserters were killed at the hands of security forces, five of them under torture, the Local Coordination Committees, the main activist group spurring protests on the ground, said.

The Arab League is putting on hold a decision to send new observers to Syria after three monitors were slightly wounded in an attack this week, an official at the Cairo-based bloc said on Wednesday.

The official also dismissed remarks by an Algerian monitor who said he quit the Syria mission, accusing the regime of war crimes, saying all his claims were unfounded because he was bedridden and was never in the field.

A French journalist was killed on Wednesday in the flashpoint central Syrian city of Homs, the first Western journalist to be killed since protests erupted in March.

The public France 2 channel identified the slain journalist as Gilles Jacquier, one of its reporters. The 43-year-old joined public television in 1991 and was an award-winning veteran who had covered conflicts in Iraq, Afghanistan, Kosovo and Israel.

Clashes between Egyptian troops and Bedouin in the Suez district east of Cairo killed three people on Wednesday as military police tried to evict the Bedouin from state-owned land, security sources said.

An officer, a conscript and a Bedouin died in a gunfight which erupted at dawn in the town of Janifah near the southern edge of the Suez Canal, the sources said.

President Bashar Assad made a rare public appearance on Wednesday, vowing to defeat a "conspiracy" against Syria a day after he blamed foreign interests for stoking months of deadly violence.

"Without a doubt we will defeat the conspiracy, which is nearing its end and will also be the end for (the conspirators) and their plans," Assad told tens of thousands of cheering supporters in the capital's central Omayyad Square.

An Arab League observer in unrest-swept Syria said Wednesday he has quit the mission, accusing the regime of committing a series of war crimes against its people and of duping his colleagues.

"I withdrew from the Arab observers mission because I found myself serving the regime, and not part of an independent observer group," Anwar Malek told the Doha-based news channel Al-Jazeera.

Cypriot authorities released on Wednesday a cargo ship carrying tons of munitions after receiving confirmation the vessel would not proceed to Syria as originally scheduled.

The ship called into Limassol port for refueling on Tuesday following bad weather, said government spokesman Stefanos Stefanou.

Hundreds of Syrian and international activists will try to cross into Syria from Turkey and Jordan on Thursday in a bid to take humanitarian aid to the Syrian people, various sources said.

"Our aim is ... to deliver humanitarian aid to the families in the afflicted areas that suffer from daily brutal bombing and totally unacceptable living conditions," said a statement posted on the website of the group called "Freedom Convoy".