The U.N. human rights chief is calling for an independent investigation into last week's slaughter of dozens of civilians in the Syrian town of Houla, as activists on Friday reported the killing of at least 12 more civilians.

Navi Pillay's comments were provided in a statement to the U.N. Human Rights Council during an emergency session Friday in Geneva on the May 25 massacre that killed at least 108 people – nearly half of them children. She called for the Syrian government to provide full access to investigators to look into the killings, which could constitute crimes against humanity.

The killings in Houla have sparked widespread outrage, with some leading diplomats calling for an international coalition to remove Syrian President Bashar al-Assad from power.

Russian President Vladimir Putin Friday again rejected the use of the force in Syria, though he told reporters Moscow was seeing “emerging elements of a civil war.” Putin spoke in Berlin following a meeting with German Chancellor Angela Merkel.

The two put out a joint statement “pushing for a political solution” with a cease-fire brokered by U.N. and Arab League envoy Kofi Annan as the starting point.

But the former U.N. secretary-general himself is voicing concerns about his plan. Speaking to reporters in Beirut, Annan said he is “impatient and frustrated” by the slow implementation of his peace plan, first put forward six weeks ago.

U.N. Secretary General Ban Ki-moon has warned continued violence and killing “could plunge Syria into a catastrophic civil war … from which the country would never recover.”

The U.N. Human Rights Council is debating a resolution presented by the U.S., Turkey, and Qatar that condemns the massacre, which prompted international outrage and rekindled efforts to stem Syria's 15-month-old conflict.

Meanwhile, opposition activists on Friday reported what they say is another mass killing of civilians.

Sipan Hassan of the U.K.-based Syrian Observatory for Human Rights told VOA that unidentified gunmen killed 12 workers near the town of Qusair in Homs province on Thursday.

“Twelve workers have been found shot in the head. They have been killed, but we don't know the circumstances of how they have been killed yet.”

Reports say the workers at a state-owned fertilizer plant were shot after their bus was forced to stop at a checkpoint on the outskirts of Qusair. The observatory told VOA the area has seen increased violence in recent days between opposition groups and the government.

Both the Qusair and Houla massacres occurred in Homs province, where there is significant support for the opposition.

U.N. personnel who went to Houla after last week's massacre said there were some suspicions of involvement by pro-government shabiha militiamen.

A preliminary investigation conducted by Damascus has blamed the atrocity on armed opposition groups who it said attacked families that would not join anti-government protests. Susan Rice, the U.S. ambassador to the U.N., on Thursday called the Syrian government claim “absurd.”

Also Friday, activists reported renewed fighting between the Free Syrian Army and government forces, despite the passing of a rebel commander's deadline for the Syrian government to comply with a U.N.-backed peace plan.

Earlier this week, a general in the Free Syrian Army said his forces will no longer be bound by the U.N. peace plan if the Syrian government fails to take steps to comply with it by midday Friday.

The Local Coordination Committees group said the Free Syrian Army was engaged in “violent clashes” with government forces in the suburbs of Damascus on Friday.

The government and the rebels agreed in April to a truce mediated by international envoy Annan. But the fighting has continued, with each side accusing the other of violating the deal.