Pro-regime residents blocked UN observers from reaching Syria’s Al-Haffe on Tuesday, as government forces shelled the town for an eighth day, sparking fears of an impending massacre there, monitors said.

“Residents of the pro-regime village of As-Sheer blocked the road and prevented the UN observer team from reaching Al-Haffe,” the Syrian Observatory for Human Rights said.

Observatory head Rami Abdel Rahman said people “lay down on the road blocking access to the vehicles of the observers,” who then began looking for another route into to the town, in the northwestern province of Latakia.

State television reported that the UN vehicles had run over three residents near Latakia who were trying to explain to the observers the suffering they were being subjected to by “armed terrorist groups.”

Abdel Rahman said the army was using heavy artillery against the town and nearby villages, leaving dozens wounded, while massing reinforcements in preparation for a ground assault.

Residents told AFP helicopter gunships were strafing rebel positions in Al-Haffe and said they feared a massacre if troops enter the town, considered strategic because of its proximity to Qardaha, President Bashar al-Assad’s home town.

Abdel Rahman said hundreds of rebel Free Syrian Army fighters are active in and around Al-Haffe, a town of about 30,000 people, setting the scene for a violent confrontation.

At least 52 people, including 29 civilians, have been killed in Al-Haffe in the past week, the Observatory says.

The UN Supervision Mission in Syria (UNSMIS) said it had received reports of “a large number of civilians, including women and children trapped inside the town and are trying to mediate their evacuation.”

UN chief Ban Ki-moon joined UN-Arab League peace envoy Kofi Annan in demanding that unarmed military observers from UNSMIS be allowed into Al-Haffe.

Syrian activist Sem Nassar broke down in tears as she told AFP via Skype that army tanks were parked on the edge of Al-Haffe

“They have never come this close before,” she added.

Washington voiced concerns that the regime is planning to carry out new atrocities, after the massacre of 55 people last week in Al-Kubeir and at least 108 near Houla in late May.

“The United States joins ... Kofi Annan in expressing deep alarm by reports from inside Syria that the regime may be organising another massacre,” State Department spokeswoman Victoria Nuland said in Washington.

The French foreign ministry spokesman on Tuesday echoed the US warnings:

“We share concerns about the preparation of new massacres,” Bernard Valero said, adding that “we more than ever support the Annan plan.”

The Britain-based Observatory said troops also pounded a neighbourhood of the eastern city of Deir Ezzor with mortar fire on Tuesday, killing 10 civilians including a young girl, and that five more civilians were killed in attacks on the central city of Homs.

An activist in Homs who identified himself as Abu Bilal told AFP via Skype that 400 civilians were trapped in a school in the Jourat al-Shiah neighbourhood.

“There are no fighters there, but still it’s being shelled,” he said.

Meanwhile, the UN accused Syrian troops of using children as “human shields”, as it branded Damascus one of the worst offenders on its annual “list of shame” of conflict countries.

Syrian children as young as nine had been victims of killing and maiming, arbitrary arrest, detention, torture and ill-treatment, including sexual violence, a report said.

“Rarely, have I seen such brutality against children as in Syria, where girls and boys are detained, tortured, executed, and used as human shields,” Radhika Coomaraswamy, UN special representative for children in armed conflict, told AFP.

Britain said Syria must offer unrestricted access to aid agencies, saying the humanitarian situation in the country is expected to worsen with thousands more likely to flee the bloodshed.

Accusing the regime of committing “serious human rights violations” against its own people, Minister of International Development Alan Duncan urged Damascus to “give unrestricted access for humanitarian agencies to help those in need.”

Annan, who brokered a faltering six-point plan, wants to bring together world and regional powers to put pressure on Syria’s leader, his spokesman said on Tuesday.

Diplomats said Annan sees the five permanent members of the UN Security Council — Britain, China, France, Russia and United States — taking part along with Iran, Turkey, Saudi Arabia, Qatar and others.

More than 14,100 people have been killed in Syria since the anti-regime revolt erupted in March 2011, according to the Observatory.