By Marwan Makdesi
HOMS, Syria, May 9 (Reuters) - Around 270 Syrian rebels granted safe exit under a complex deal with President Bashar al-Assad's forces are being held in Homs by the army after insurgents elsewhere failed to uphold their side of the agreement, Syrian officials said on Friday.
Following a year of siege, around 1,200 rebels and residents in the Old City of Homs left the city on buses this week in exchange for the release of dozens of captives held by rebels in the northern provinces of Aleppo and Latakia.
Officials said rebels had also agreed to allow aid into two northern Shi'ite towns besieged by the opposition, Nubl and al-Zahraa, but as of Friday a convoy of food and medical relief was stuck at insurgent checkpoints outside the towns.
The officials, who spoke on condition of anonymity, said that the remaining 270 rebels will only be let out of Homs when the aid reaches Nubl and Zahraa.
They did not specify which groups had prevented the relief from entering. Activists said Syria's al Qaeda offshoot, the Nusra Front, blocked aid convoys to Nubl and Zahraa on Wednesday, but other armed rebels are also active in the area.
More than 150,000 people have been killed in the conflict, which has become increasingly sectarian as rival regional powers have backed either Assad, a member of the Shi'ite offshoot Alawite sect, or the overwhelmingly Sunni rebels who oppose him.
Millions more have fled their homes and fighting regularly kills more than 200 people a day.
The fall of Syria's third largest city to government forces is a major blow to the opposition and a boost for Assad, weeks before his likely re-election. (Writing by Oliver Holmes; Editing by Catherine Evans)