Muslim clerics in Syria have issued a fatwa permitting people to eat cats, dogs and donkeys, as graphic new footage shows the effects of malnutrition on starving children caught up in the country's civil war.

The ruling has been broadcast from mosques in besieged areas on the outskirts of Damascus.

Much of the area is under the control of rebels, triggering daily bombardments from government forces trying to win it back.

Government forces have also tried to block food and other relief supplies getting through.

The clerics say it is a cry for help to the whole world, adding that if the situation continues to deteriorate, the living could have to eat the dead.

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The drastic measure comes as Muslims around the world mark the Eid al-Adha holiday, sharing festive meals.

For Muslims, Eid is a time for children to receive new clothes and play with friends after sharing a festive meal with their families.

But in some areas of Damascus, children have died from severe malnutrition and activists say food has all but run out, with doctors lacking the means to treat their patients.

"Of course there is no Eid for the children here," activist Abu Malek said in Moadamiyet al-Sham, a suburb south-west of Damascus.

"For them, Eid will come when they see a plate of rice and bulgur."

Graphic video footage shows malnourished children dying

Shocking amateur videos have been distributed by activists from the town, showing visibly malnourished children.

One video shows a boy, identified as Ibrahim Khalil, laid out on a stretcher.

His ribs and cheekbones protrude from underneath his pale skin, and he has dark circles surround his eyes.

Another video shows a girl with her two baby siblings, appealing for help so her family can secure baby milk.

"There is no road... the road is closed... what are we going to do?... we are feeding them milk but it's expired," says the little girl, as the babies cry.

For some, relief came earlier this week, when the International Committee of the Red Cross and the Syrian Red Crescent evacuated 3,500 people from Moadimayet al-Sham with the agreement of the authorities.

But only children, women and old men were able to leave, with the wounded left behind and aid workers prevented from entering the area.

"There are many more, including children, who remain in the town," Magne Barth, head of the ICRC delegation in Syria, said.

The situation is just as bad for children in other rebel-held areas near Damascus.

"On any given day in the emergency room, some four out of 10 patients I see are malnourished children," said Abu Mohammad, a doctor working in a field clinic in the Marj area east of the capital.

"Many children have very low blood pressure, fatigue, dizziness, and a reduced (disease-fighting) white blood cell count.

"The worst affected by the food shortages are children aged under two years."

Doctors lack food, medical equipment to treat patients

He said the hardest part is not having the right medical equipment or food to fight malnutrition.

"I get depressed in the clinic, because we don't have what we need to fight this," he said.

Also affected is Yarmuk, a Palestinian refugee camp in southern Damascus which has turned into a battleground in recent months.

"Nothing, not even bread or flour, has been allowed in for 96 days," said Palestinian-Syrian activist Ali Abu Khaled, who added that he was "lucky to get one small meal a day".

Speaking to AFP on the eve of Eid, a cleric in southern Damascus said a man in his area recently ate dog meat out of desperation.

"We issued a religious edict allowing people to eat dog and cat meat. Not because it is religiously permitted, but because it is a reflection of the reality we are suffering," said Sheikh Saleh al-Khatib, who has been on hunger strike for nine days.

"People here have nothing for their children.

"I am on strike because I want to help save food for others."

Residents survive by planting herbs, vegetables

Syrian children search for belongings at a bomb site in the Duma neighbourhood of Damascus last month. ( Reuters: Bassam Khabieh )

In Moadamiyet al-Sham, people are surviving on herbs and vegetables they have planted.

"We no longer have any food in the stockpiles. Everyone is planting in the orchards and the streets," said activist Abu Hadi, adding that no bread had entered the area for months.

But harvesting the food is dangerous, "and people have died in the orchards because of the shelling", he said.

Rami Abdel Rahman, director of the Syrian Observatory for Human Rights, said many children in Moadamiyet al-Sham are malnourished.

"Children are worst off because they need the right kinds of food in order to grow," he said.

"Adults can survive on whatever they can find, but what about the children?"

The army says "terrorists," its term for the rebels, have trapped civilians against their will.

But activists accuse the military of using the siege to try to turn people against the rebels.

"It is a war crime to besiege civilians," Abdel Rahman said.

Video claims Syria's first lady standing by president

Meanwhile, Syria's first lady Asma al-Assad laughed off claims she has fled the war-hit country in footage broadcast on Tuesday, saying she was standing by her embattled husband president Bashar al-Assad.

A Syrian state TV clip shows first lady Asma al-Assad (L) speaking with a woman at an undisclosed location. ( AFP/Syrian TV )

The British-educated Ms Assad has rarely appeared in public since the beginning of the conflict in Syria, where more than 115,000 people have been killed since March 2011 according to a watchdog.

But on Tuesday, hours after her husband attended prayers to mark the Muslim Eid al-Adha feast in Damascus, Syrian state television broadcast a clip of the first lady.

The mini-feature showed her comforting the bereaved and planting olive trees with children, dressed in black trousers and a grey T-shirt with the Syrian flag on the front.

"I am here, my husband and my children are here in Syria. It's obvious that I'd be here with them," she told reporters, when asked about claims that she had left the country.

"How can I teach my children to love Syria if they don't live here?" she added with a smile.

"I was here yesterday, I'm here today and I will be here tomorrow."

ABC/wires