International peace envoy Kofi Annan has begun talks with Syrian President Bashar al-Assad in Damascus to urge compliance with a cease-fire that he mediated between government and rebel forces last month.

A U.N. spokeswoman in the Syrian capital told VOA that Mr. Annan would raise two main issues in Tuesday's meeting: his six-point peace plan for Syria and the killings of at least 108 civilians in the rebellious town of Houla last Friday.

The U.N. human rights office in Geneva said Tuesday U.N. monitors found that fewer than 20 of those killed in Houla were struck by artillery and tank fire. It said witnesses told the observers that most of the other victims were killed in two waves of summary executions by pro-government militiamen.

After arriving in Damascus on Monday, the former U.N. secretary-general said he was “shocked and horrified” by the Houla massacre, calling it “an appalling crime.” The U.N. Security Council issued a statement a day earlier blaming some of the deaths directly on “government artillery and tank shellings.” The statement also condemned shootings and stabbings of the other victims but did not say who was responsible.

U.N. spokeswoman Sausan Ghosheh said U.N. observers have remained in Houla since Saturday and have been talking to residents to establish the facts.

The Syrian government denies any role in the Houla killings and blames all of them on “armed terrorists” whom it accuses of driving a 15-month revolt against Mr. Assad.

Ghosheh also said U.N. monitors have not been able to get into a district of Hama city where activists said government forces bombarded residential areas from Sunday into Monday in retaliation for rebel attacks. She said security problems were preventing observers stationed in Hama from entering the Arbeen district to check on activist reports that more than 34 civilians were killed in the fighting.

Speaking on Monday, Mr. Annan appealed to “everyone with a gun” in Syria to resolve the country's conflict peacefully. Government and rebel forces have continued fighting each other despite accepting a truce that he brokered in April.

Australia expelled two Syrian diplomats from Canberra on Tuesday in protest at the Syrian government's perceived role in the Houla massacre. Australian Foreign Minister Bob Carr said he expects other countries will do the same in the coming days.

A Vatican statement issued Monday said Pope Benedict was “pained” by the Houla killings and called on the international community to “spare no effort” to end the Syrian crisis through “dialogue and reconciliation.”

The office of British Prime Minister David Cameron said he and French President Francois Hollande have agreed to increase international pressure on the Assad government to end what they consider to be the “bloody suppression of the Syrian people.” Mr. Cameron and Mr. Hollande discussed the crisis in a Monday phone call.

The two leaders also reiterated their support for Mr. Annan's peace mission in Syria and agreed to work with Syrian ally Russia to find a resolution to the conflict.

Russian Foreign Minister Sergei Lavrov said Monday that evidence indicates Syrian government and rebel forces both are to blame for the Houla massacre. Russia previously has shielded President Assad from U.N. sanctions sought by Western and Arab nations opposed to his 11-year rule, but Moscow recently has toughened its criticism of the Syrian leader's handling of the uprising.

In Washington, the chairman of the Joint Chiefs of Staff, General Martin Dempsey, warned that “atrocities” such as the Houla killings could trigger international military intervention. But, he also stressed that the international community should exert greater diplomatic pressure on Mr. Assad before exploring military options.

The United Nations says more than 10,000 people have been killed in Syria since the government began its crackdown on dissent in March 2011.