A Syrian female refugee's self-immolation in front of the UN headquarters in the Lebanese capital has highlighted the plight of nearly 2.6 million people who have fled from Syria.

Mariam al-Khawli, who fled her county with her husband and four children two years ago, set herself on fire last week out of frustration over living without food and cash lifeline after a UN cutback.

Khawli’s doctor, Gabriel al-Sabeh, said 70 percent of her body was now covered in burns and that she could remain in hospital for months if she survives.

Khawli’s husband is unable to work due to a lung abscess and three of her children have a blood condition and had relied on the aid, which had stopped in August. Her story has become well known over the past days, after appearing in news outlets in Lebanon.

"We really got hungry, but they burned my heart before they burned my body. They burned my heart from the inside," Khawli told Reuters news agency of how she regarded the UN cutback.

Officials at the UN headquarters in Beirut blamed a lack of funding for the limited aid provided to those who fled the violence.

Million Syrian refugees

The number of Syrians registered as refugees in Lebanon surpassed one million on Thursday, the UN refugee agency said.

The influx of a million refugees would be massive in any country. For Lebanon, a small nation beset by internal difficulties, the impact is staggering, Antonio Guterres, UNHCR chief

Refugees from Syria now equal a quarter of Lebanon's resident population, the UNHCR said, describing the figure as "a devastating milestone worsened by rapidly depleting resources and a host community stretched to breaking point".

Lebanon has now become the country with "the highest per capita concentration of refugees worldwide," said the UNHCR, adding that is "struggling to keep pace".

"The influx of a million refugees would be massive in any country. For Lebanon, a small nation beset by internal difficulties, the impact is staggering," UNHCR chief Antonio Guterres said in a statement.

Ninette Kelley, regional representative for Lebanon at the Office of the UN High Commissioner for Refugees, said Khawli's case was "a very sorrowful reflection of the enormous desperation and need of the refugee community and it is also a telling reminder of the consequences of the Syrian emergency and the unfolding crisis here in Lebanon".

Kelley said the agency had been in touch with Khawli's family "for many, many months", but gave no details of why the funds were cut or how many other families might have been affected.

UN aid teams in Lebanon give aid to the most vulnerable first and makes regular checks on families who are not covered, Kelley said.

Last month, Lebanon's foreign minister said the crisis was "threatening the existence of Lebanon", still recovering from its own bloody 15-year civil war that ended in 1990, and called for their redistribution among other countries, citing depleted resources and infrastructure.

Syrian beggars now walk the streets of Beirut and informal tented settlements have sprung up around the country.

Lebanon has fallen in a wave of violence as political and religious sects took rival sides in the war in Syria, where Sunni Muslim rebels are fighting against President Bashar al-Assad, who is from the Alawite minority.

Lebanon holds the largest number of asylum seeker, but Syrians have also fled to Turkey, Jordan, Iraq, Egypt and elsewhere.

A UN appeal for $1.7bn in 2014 to help the refugees is only 14 percent funded, Kelley said.