Al-Qaeda in Iraq claims deadly attack on Syrian troops
A militant umbrella group that includes al-Qaeda in Iraq has said it was behind the killing of 48 Syrian soldiers and nine Iraqi guards in Iraq last week.
In an online statement, the Islamic State of Iraq said its fighters had set ambushes on roads to the border and "annihilated" an entire convoy.
The presence of Syrian troops showed Iraqi leaders' "firm co-operation" with President Bashar al-Assad, it added.
Meanwhile, the UN has announced it has evidence of further massacres in Syria.
In a new report for the Human Rights Council, the Independent International Commission of Inquiry (CoI) on Syria accused both government and opposition forces of showing a reckless disregard for the lives of civilians across the country.
Investigators found evidence of three massacres in the central city of Homs between December and March. In one, 50 prisoners were executed by government forces, while in the other two entire families were killed in their homes, though it remains unclear by whom.
The report says that fighting has spread right across Syria and that nowhere is safe for civilians. Basic human rights like access to food, medicine and education have all but disappeared, it adds.
It calls for those responsible for war crimes to be brought to justice, but only the UN Security Council can refer a country to the International Criminal Court (ICC) if it is not party to the Rome Statute, and the Security Council remains divided, the BBC's Imogen Foulkes in Geneva says.
The Syrian soldiers who were killed in Iraq last week reportedly entered through the Yaarubiyeh border in the northern Nineveh province over the weekend of 2-3 March after Syrian rebels attacked them.
On 4 March, the soldiers were being escorted to the al-Waleed border crossing further south in Anbar province when they were ambushed near the town of Akashat, Iraqi officials said.
A statement posted on jihadist websites by the Islamic State of Iraq on Monday claimed that its military detachments had "succeeded in annihilating an entire column of the Safavid army", a reference to the Shia dynasty which ruled Iran between the 16th and 18th centuries.
President Assad's Alawite sect is a heterodox offshoot of Shia Islam.
The assailants detonated explosive charges on military escort vehicles assigned to protect the lorries carrying the Syrian soldiers, then opened fire with "light and medium-range weapons, as well as rocket-propelled grenades", the statement added.
The Sunni Islamist group also said the presence of Syrian forces showed the "firm co-operation" of Iraq's Shia-led government with Syria's president.
Syria's majority Sunni community has been at the forefront of the uprising against the state, which the UN says has left 70,000 people dead.
Iraqi Prime Minister Nouri Maliki has said he is taking no sides and blamed last week's attack on Syrian armed groups which had infiltrated his country.
He has previously expressed concern that the two-year-long conflict in Syria could spill over the 600km (372-mile) shared border.