Geneva - UN observers have been moved out of the besieged Syrian city of Aleppo because of worsening security, a UN spokesperson said on Monday.
The approximately 20 unarmed observers were moved back to the mission's Damascus headquarters at the weekend.
"It is a temporary relocation because of the deteriorating security," Josephine Guerrero, a UN peacekeeping spokesperson, said.
President Bashar Assad's forces have stepped up shelling of rebel-held districts of Aleppo in recent days. Hundreds have been killed in the city in the past two weeks, according to activists.
Aleppo was one of four regional bases where the UN Supervision Mission in Syria (UNSMIS) had retained teams, even though their main activities have been suspended since June. There are also UN offices in Deir Ezzor, Homs and Rif Damascus, which is in the capital's suburbs.
The UN has halved the number of observers in Syria to about 150 since last month. The UNSMIS mandate ends on 20 August and the UN Security Council has yet to agree on the future UN presence in the country.
UNSMIS's interim chief Lieutenant General Babacar Gaye said on Monday that the civil war is worsening and expressed particular concern over Aleppo.
"I am extremely concerned about the continued violence in Syria in particular the significant deterioration in Aleppo and its impact on the civilian population," Gaye said in a statement.
"I urge the parties to protect civilians and respect their obligations under international humanitarian law. Civilians must not be subjected to shelling and use of heavy weapons," Gaye added, renewing calls for "dialogue" between the government and opposition.