Rana, a refugee in Lebanon who would not give her full name, said she had been forced to pay a bribe to cross the border. "Security forces were attacking my neighbourhood in Aleppo," she said. "I fled with nothing but I had to pay $40 dollars to be allowed to cross." 

A number of opposition activists abroad say their families inside the country have been taken away or beaten up in retaliation, while defecting members of the regime's army have described waiting until they were able to accompany their families abroad before crossing over, earlier in the uprising.

But tens of thousands of refugees are continuing to try to leave, despite the current supposed ceasefire and peace plan put forward by the UN envoy, Kofi Annan.

Yesterday, a visit by members of the UN monitoring mission withdrew from Arbeen, a Damascus suburb, after troops started shooting at a crowd of protesters, activists said.

The Syrian authorities yesterday said they were drawing up a "protocol" with the monitors to allow the arrival of the main party, supposed to consist of 250 peacekeepers.

The flow of refugees to Jordan and Lebanon, which have been trying to remain neutral in the conflict, is particularly worrying for the regime.

Mr Abu Saleh said it had become "common" for families to be refused exit at the Masnaa border crossing between Beirut and Damascus. An activist in Jordan said there were now 4,000 families, mostly from Homs, near the border at Jaber, many sleeping in the open and some with families.

The authorities are only allowing those over 60 to cross, unless bribes are paid, and no children, the activist said, adding that the regime was keen to stop numbers of refugees inside Jordan, which already stand at 100,000, reaching 150,000. "That would be a major embarrassment for Bashar," he said.

Mousab Azzawi, of the London-based Syrian Network for Human Rights, said the regime had reactivated old laws under which a woman leaving the country without her husband needed a letter of approval from him, certified by a judge and the security forces.

"In past years this has not been enforced and woman and children could cross freely," he said. "Now they use it - it is a lengthy process that amounts to a ban," said Azzawi.

Aside from bureaucratic constraints, activists reported seemingly arbitrary excuses being given by border officials. Mr Abu Salah's aunt and uncle were told they could not leave the country with their child as he had to attend school in Syria.

"Officials said they should get papers from the education ministry to leave the country," he said. "But they are from Homs, there are no schools open there anymore.

"My brother's fiancee wanted to come to Lebanon with her family. They were turned back. 'Go away and shut up', the border guards told them."

Further Information:

• SYRIA: Rebels accused of using child soldiers (29 March 2012) 
• SYRIA: Authorities systematically targeting children (28 March 2012) 
• SYRIA: Villagers 'forced into human shield for Assad's soldiers' (25 March 2012)
• SYRIA: Whole city besieged to "wipe out pockets of armed terrorists” (22 February 2012) 
• SYRIA: SRSG Coomaraswamy calls to immediately halt all violations against children (9 February 2012) 
• SYRIA: Children severely tortured in detention (3 February 2012) 
• SYRIA: Remembering child victims of military crackdown (17 January 2012)
• SYRIA: 6,200 killed, including 400 children (9 January 2012) 
• SYRIA: Boy, 10, slain in home by sniper (12 December 2011) 
• SYRIA: Assad denies responsibility for the killing of thousands of anti-government protesters (7 December 2011)
• SYRIA: Children's rights violations feature in Special Session on Syria (2 December 2011) 
• SYRIA: UN rights panel voices alarm at reported torture of children (25 November 2011)
• SYRIA: Wave of violence targets children (23 November 2011) 
• SYRIA: Three children among latest killed (28 October 2011) 
• SYRIA: Concerns over “rampant torture” (7 October 2011)
• SYRIA: New report indicates over 5,000 deaths since March, including 148 children (Avvaz, 22 September 2011)
• SYRIA: Death toll tops 2,700, including 100 children (20 September 2011) 
• SYRIA: Boy, 12, shot dead during funeral procession (13 September 2011) 
• SYRIA: Teen killed as protesters call for international protection (9 September 2011) 
• SYRIA: Amnesty report shows 88 civilians killed in detention, including 10 children (31 August 2011) 
• SYRIA: A child's killing freeze-frames tragedy (17 August 2011) 
• SYRIA: Defectors describe orders to shoot unarmed protesters (18 July 2011) 
• SYRIA: Second teenager tortured to death (16 June 2011) 
• SYRIA: Soldier 'ordered to fire' on peaceful protesters (10 June 2011)
• More on children's rights in Syria