BEIRUT: Syria's civil war is unleashing a "staggering humanitarian disaster", sending hundreds of thousands of refugees fleeing to neighbouring countries, many of them citing fear of rape, an aid agency said on Monday.

The New York-based International Rescue Committee (IRC) said Syrian refugees interviewed in Lebanon and Jordan gave sexual violence as a primary reason for their flight, saying that gang rapes often occur in front of family members.

"After decades of working in war and disaster zones, the IRC knows that women and girls suffer physical and sexual violence in every conflict. Syria is no exception," the IRC said in a 23-page report entitled "Syria: a regional crisis".

"Many women and girls relayed accounts of being attacked in public or in their homes, primarily by armed men," it added, without identifying those responsible.

Both rebels and government forces have been accused of human rights abuses during the 21-month-old conflict.

The IRC said it was also told of attacks in which women and girls were kidnapped, raped, tortured and killed.

"For survivors who manage to flee, there is a shortage of medical and counselling services to help them recover in the communities where they have settled and even there, challenges continue. Many women and girls face unsafe conditions in refugee camps as well as elevated levels of domestic violence."

The crisis began with peaceful protests against Syrian President Bashar al-Assad but turned violent after his forces shot at demonstrators. It is now a full-scale armed conflict in which the United Nations says has cost more than 60,000 lives.

"Nearly two years into Syria's civil war, the region faces a staggering humanitarian disaster, requiring the international community to urgently scale up planning and funding for what is certain to be a long-term regional crisis," the IRC said.

"Preparations must be made for a mass exodus of refugees, should there be a sudden escalation of the crisis," it said, calling on host countries to keep their borders open.

This has been a sensitive issue in Lebanon, which has taken in more than 190,000 Syrian refugees. Some Lebanese politicians have suggested shutting the frontier to halt the influx.

More than 600,000 Syrians have fled abroad and the United Nations says a continued exodus could soon swell the number to a million. More than 2 million civilians are internally displaced and 4 million are in dire need of assistance, it says.

The IRC said the humanitarian emergency could last for years, urging donor governments to meet a $1.5 billon U.N. funding appeal and help host countries offset the strain on their infrastructure and mitigate growing tension.

The Syrian government has been accused of restricting access to international aid organisations. The IRC said partnerships with Syrian aid organisations should be expanded.

In addition to air strikes and street battles, Syrians report severe power outages, a lack of medicine, food and water. As winter takes hold, many are without heating. Entire neighbourhoods have been reduced to rubble.

The IRC said Syrian physicians reported "a systematic campaign to restrict access to lifesaving care through the strategic bombing and forced closure of medical facilities" and "intimidation, torture and the targeted killing of doctors in retribution for treating the wounded".