The revered Sayyida Zeinab shrine near Damascus has become a symbol of the bloody sectarian fault line in Syria's war, targeted by Sunni jihadists and used as a rallying call by Shiite groups.

For years, thousands of Shiite Muslims have visited the sacred site each day, circling the courtyard and chanting religious hymns.

But with the eruption of Syria's war in 2011, Sayyida Zeinab now lies at the heart of the brutal conflict.

A string of devastating bomb attacks near the site on Sunday, claimed by the Islamic State (IS) jihadist group, killed 120 people, including at least 90 civilians, the Syrian Observatory for Human Rights said.

The rest of the dead were from pro-regime security forces guarding the site.

The shrine lies in a densely-populated area about 10 kilometres (six miles) south of Damascus and contains the grave of Zeinab, a much-venerated granddaughter of the Prophet Mohammed.

Zeinab is the daughter of Ali, son-in-law of Mohammed and a figure held in high esteem by Shiite Muslims worldwide.

 Apple said Monday it would accept having a panel of experts consider access to encrypted devices if US authorities drop legal efforts to force it to help break into the iPhone of one of the San Bernardino attackers.

In a statement posted on its website, Apple reaffirmed its opposition to the US government's effort to compel it to provide technical assistance to the FBI investigation of the deadly December attacks, but also suggested a compromise in the highly charged court battle.

"We feel the best way forward would be for the government to withdraw its demands under the All Writs Act and, as some in Congress have proposed, form a commission or other panel of experts on intelligence, technology and civil liberties to discuss the implications for law enforcement, national security, privacy and personal freedoms," the statement said.

"Apple would gladly participate in such an effort."

A magistrate this month ordered Apple to provide technical assistance to the FBI under the 1789 All Writs Act, which lays out broad authority for the courts to help enforcement of the law.

Apple's statement -- the latest volley in the escalating legal and public relations battle over encryption -- said enforcing the court order "would set a legal precedent that would expand the powers of the government and we simply don't know where that would lead us."

The statement added: "Yes, it is certainly possible to create an entirely new operating system to undermine our security features... But it's something we believe is too dangerous to do. The only way to guarantee that such a powerful tool isn't abused and doesn't fall into the wrong hands is to never create it."
Apple also said it has offered advice to the FBI but that investigators made an error which made it more difficult to access the iPhone data through the backup known as the iCloud.

"We learned that while the attacker's iPhone was in FBI custody the Apple ID password associated with the phone was changed," the statement said.

"Changing this password meant the phone could no longer access iCloud services."

In a memo to Apple employees also released Monday, chief executive Tim Cook said the tech giant was not willing to roll back security features included in its new phones and software, which allow only the user to unlock the devices.

"This case is about much more than a single phone or a single investigation," Cook said.

"At stake is the data security of hundreds of millions of law-abiding people, and setting a dangerous precedent that threatens everyone's civil liberties."

The Apple response came just hours after FBI Director James Comey explained the government's position, saying it was about "the victims and justice" in the attack that killed 14 people in California, carried out by a couple believed to have been inspired by the Islamic State group.

"We don't want to break anyone's encryption or set a master key loose on the land," Comey said in a posting that appeared on the Lawfare blog and on the FBI website.

"The San Bernardino litigation isn't about trying to set a precedent or send any kind of message," Comey said.

"It is about the victims and justice."

According to Comey, the "particular legal issue is actually quite narrow... We simply want the chance, with a search warrant, to try to guess the terrorist's passcode without the phone essentially self-destructing and without it taking a decade to guess correctly. That's it."

The case has led to battle lines drawn, with many tech firms and encryption experts backing Apple and law enforcement supporters siding with the government.

The issue has even spilled into the presidential campaign, with Republican frontrunner Donald Trump calling for a boycott of Apple until the tech giant complies with US government demands.