Turkey has protested after Syrian forces opened fire across the border, in the first such attack since Turkey began housing refugees from the unrest.

Ankara summoned Syria’s envoy after two incidents in which violence spilled over into Turkey, leaving at least two people dead and many injured.

Separately, a Lebanese cameraman was shot dead on the Syria-Lebanon border.

The violence comes amid fading hopes that a UN-brokered Syria ceasefire will start on Tuesday as planned.

Monday has proved to be one of the bloodiest days of the uprising despite the truce deal, which should be marked by troop withdrawals from towns and cities if it is being implemented.

Activists reported more than 100 deaths – among them at least 30 civilians who died during Syrian army bombardment in the central province of Hama.

Harrowing scenes were reported in the town of al-Latmana, where 17 women and eight children were said to have been crushed under the rubble of their homes in the second attack on the area in days.

The deaths come as a report by Human Rights Watch accused Syrian forces of carrying out more than 100 summary executions since March. The report says most of the victims were civilians.

Annan visit

In the second incident two Syrian refugees and a Turkish translator were wounded inside a refugee camp after being hit by stray bullets from clashes between Syrian rebels and troops, according to Turkey’s foreign affairs ministry.

Turkey summoned Syria’s envoy to demand an immediate halt to such violence.

In a separate incident, a Lebanese cameraman for Lebanon’s Al-Jadeed television channel was shot dead amid gunfire in the border region between Syria and Lebanon’s northern Wadi Khaled district.

Ali Shaaban was killed and a colleague injured when a film crew from Al-Jadeed came under a hail of bullets from troops on the Syrian side of the border.

Lebanon’s prime minister condemned the killing of Mr Shaaban.

The BBC’s Jonathan Head, on the Turkey-Syria border, says the Syrian army has been careful to keep away from the border but that seems to have broken down this time.

He says incidents like this have inflamed emotions in Turkey and the Turkish government has almost given up on the ceasefire plan, brokered by UN-Arab League envoy Kofi Annan.

Turkey has seen a sharp rise in the number of refugees coming over the border in the past week, and now hosts some 24,000 Syrians, including hundreds of army defectors.

Mr Annan will briefly visit Syrian refugees on the Turkish border on Tuesday, reports say.

Deadline ‘void’

However, there are now serious doubts about whether Mr Annan’s ceasefire plan will come into effect on its Tuesday deadline.

It said it did not want the rebels to exploit any troop withdrawal to reorganise and rearm themselves. The rebel Free Syrian Army said although it backed the UN-Arab League truce, it refused to meet the government’s new demands.

Brazilian diplomat Paulo Pinheiro, who is chairing a UN inquiry into the Syrian conflict, said the demands made by Syria were almost “impossible” to meet.

“I think that everybody in the world is worried that at the eve of the deadline, the government of Syria – instead of preparing to retreat – has escalated the military offensive,” Mr Pinheiro said.

China on Monday called on the government and opposition in Syria to “honour their commitment of ceasefire and withdrawal of troops”. But correspondents say Russia, Syria’s main ally, may now have to play a crucial role. Syrian Foreign Minister Walid Muallem is in Moscow for talks.

The UN says more than 9,000 people have been killed in the uprising against Mr Assad’s rule which began more than a year ago.

The Syrian government says 2,000 security personnel have been killed in the uprising and blames the violence on “armed gangs” and “terrorists”.

Jim Muir BBC News, Beirut

Turkey is furious at the latest violence spilling over the border from Syria. These are serious incidents which will exacerbate already high political tensions between Turkey and Syria.

Turkey’s Prime Minister Recep Tayyip Erdogan is already very concerned about the conduct of the counter-insurgency in Syria. He has strongly insisted on changes by the Syrian government and is gravely disappointed with his former ally, President Bashar al-Assad.

President Assad is facing growing pressure from Turkey for some kind of action, perhaps involving a protected buffer zone or corridor, inside Syria.

It is all speculation at the moment, but this is the kind of thinking that could emerge the more we have these kinds of incidents and the more the peace process in Syria stumbles.