Violence has spilled over into Turkey, Lebanon and Israel. And the conflict has become entangled in issues involving another hot-button nation in the Middle East: Iran.
On Friday, France's foreign ministry issued a statement opposing Iran's participation in an international peace conference on Syria.
Iran has been a strong ally of al-Assad and his government, as well as a focus of international condemnation over its nuclear program.
"The stability of the whole region is in question," the French ministry said. "We can't see a country, representing a threat to stability, taking part in this conference."
The French government said that Tehran should provide a "certain number of answers" and meet "international obligations" before it takes part in talks regarding Syria.
Gruesome footage shows man cutting out soldier's organs
Inside Syria itself, opposition groups responded Friday to widespread outrage this week over a horrific video showing a man said to be a Syrian rebel carving into the body of a government soldier, cutting out his heart and liver, and taking a bite of the heart.
The Syrian Observatory for Human Rights, a London-based activist group, questioned in a statement why the world had not paid the same attention to the many videos it has published showing atrocities allegedly carried out by forces loyal to al-Assad.
A new video purported to be of the Syrian rebel who carried out the atrocity, Khaled al-Hamad, known as Abu Sakkar, was also posted online Friday.
He is asked, "Abu Sakkar, do you regret what you have done? After the killing of the Assad militiaman and the mutilation of his body?"
He replies: "I am ready to face justice and be brought to trial for my actions on the condition that they need to bring Bashar and his thugs to stand trial as well, for the atrocities that they have committed against our women and children."
He warns that "if the bloodshed doesn't stop in Syria, all of the Syrian people will be Abu Sakkar. Everyone will be Abu Sakkar."
Although CNN cannot independently verify the authenticity of the videos, it interviewed a local rebel spokesman this week who confirmed the heart-eating incident and said he had spoken to the man involved.
Also Friday, Human Rights Watch urged the rebel groups now in control of Raqqa city, in northern Syria, to ensure that evidence of torture chambers in government security facilities seen by HRW researchers last month is preserved.
"The documents, prison cells, interrogation rooms, and torture devices we saw in the government's security facilities are consistent with the torture former detainees have described to us since the beginning of the uprising in Syria," said Nadim Houry, deputy Middle East director at Human Rights Watch.
"Those in control of Raqqa need to safeguard the materials in these facilities so the truth can be told and those responsible held accountable."