(Adds detail from hospital officials, background)
By Ahmed Elumami
TRIPOLI, June 12 (Reuters) - A suicide bomber killed three people at a field hospital for forces fighting Islamic State in their Libyan coastal stronghold of Sirte on Sunday, a security source said, and medical staff appealed for help in treating the wounded.
The bomber also wounded seven others and caused extensive damage to the hospital, about 50 km (30 miles) from the front line, the source said. Two other attempted suicide bombings just outside the centre of Sirte did not cause casualties, he said.
Brigades aligned with the U.N.-backed Government of National Accord have made rapid advances over the past month. This week they entered Sirte, engaging Islamic State militants in street battles keeping up air strikes against them.
The brigades, made up mainly of fighters from the western city of Misrata, have faced suicide bombings, snipers and mines. At least 120 brigade members have been killed and more than 500 wounded, security and hospital officials say.
Islamic State took advantage of lawlessness and political chaos to expand into Libya from late 2014. It has launched attacks at numerous sites along Libya's Mediterranean coastline but Sirte is the only city where it has taken full control.
Officials in Misrata have long cited a lack of medical capacity to treat the wounded as a constraining factor in their efforts to fight the ultra-hardline group.
Medical facilities are overflowing in Misrata, where, for example, the waiting room of the central hospital has been turned into a makeshift ward with room for 12 patients.
"The wounded here at Misrata hospital are in a very bad state. The hospital care rooms are at full capacity, the private hospitals are also at full capacity," a medical official in Misrata, Malek al-Qualaib, said.
The hospital is running low on medical supplies and has no emergency back-up stocks, hospital spokesman, Aziz Issa, said.
"We have a lack of specialised doctors, and nurses, who left Misrata before the battle due to unpaid salaries, as well as a shortage of anaesthesia and X-ray equipment," he said.
"We appeal to the international community and international organisations to help us in providing necessary medical treatment for the wounded."
More than 150 wounded fighters have been sent abroad for treatment, to Tunisia, Turkey, Italy and Algeria, but the departure of some wounded fighters had been delayed or prevented because they had not received visas, Issa said.
Qualaib said there had also been delays because of problems getting permission for flights into European air space and because of lack of funding for evacuating the wounded. (Additional reporting by Ayman el-Sahli in Misrata; Writing by Aidan Lewis; Editing by Louise Ireland)
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