Syrian President Bashar Assad and peace envoy Kofi Annan met in Damascus on Tuesday, as the United Nations human rights office said that most of the 108 victims of the "massacre" in the town of Houla may have been summarily executed and not killed in artillery barrages as had originally been reported. Meanwhile on Tuesday, opposition sources said that Syrian insurgents killed 20 soldiers in heavy fighting around a northern Syrian town close to the border with Turkey. They said six civilians and six rebels, including two rebel commanders, were also killed over the past 24 hours in the fighting after the army launched an offensive with tanks and helicopters to retake the region around Atareb in Aleppo province, 18 km (11 miles) east of the Turkish border."I believe at this point, and I would stress we are at very preliminary stages, that under 20 of the 108 can be attributed to artillery and tank fire," he told a news briefing in Geneva.Some 49 children and 34 women were among the known victims, but the toll was not definitive, he said, adding: "There are reports of more deaths.""Almost half of the ones we know of so far are children - that is totally unpardonable - and a very large number of women as well," Colville said."At this point it looks like entire families were shot in their houses."The Syrian government has denied perpetrating the killing in Houla, blaming the assault on Islamist terrorists. "During this time, Syria has not committed a single violation of Annan's plan or the initial understanding between Syria and the United Nations," Deputy Foreign Minister Faisal Mekdad told reporters in Damascus."At the same time, the other party has not committed to a single point. This means that there is a decision by the armed groups and the opposition not to implement Annan's plan and to make it fail."The killings in Houla sparked outrage in the West, prompting many governments to expel Syrian diplomats from their capitals.Annan is attempting to salvage a six-week-old peace plan, backed by the United Nations and the Arab League, that has barely slowed the bloodshed in a 14-month-old uprising against Assad.The former UN secretary general left the presidential palace after a meeting of around two hours. Annan told Assad on Tuesday that "bold steps" were required for his six-point peace plan to succeed, including a halt to violence and release of people arrested in the uprising, a statement said."Joint Special Envoy Kofi Annan met President Bashar Assad this morning to convey the grave concern of the international community about the violence in Syria, including in particular the recent events in Houla."He conveyed in frank terms his view to President Assad that the six-point plan cannot succeed without bold steps to stop the violence and release detainees, and stressed the importance of full implementation of the plan," said the statement issued by his spokesman Ahmad Fawzi after talks in Damascus. On arrival in Damascus on Monday, Annan called on the authorities to act to end the killing after what he called the "appalling crime" late last week in the Syrian town of Houla, in which at least 108 people, almost half of them children, were killed.The United Nations human rights office said on Tuesday that fewer than 20 of the 108 people confirmed as having been killed in the massacre in the Syrian town of Houla died from artillery and tank fire, Survivors have told UN investigators that most of the other victims died in two bouts of summary executions carried out by pro-government "shabbiha" militiamen in the nearby village of Taldaou, UN rights spokesman Rupert Colville said.