Syrian troops have intensified their shelling of rebel-held neighbourhoods in the central city of Homs as living conditions there deteriorate further, according to opposition activists.
The neighbourhoods of Jouret al-Shayyah, the Old Ciy, al-Khalidiyeh and al-Hamidiyeh have been under intense shelling and ground attacks for a week.
Activist Abu Bilal in the Old City said on Sunday that the regime's siege of several parts of Homs was "suffocating".
"They are shelling us all the time. There's very little food and water, and we're running out of medication," he said.
The Britain-based Syrian Observatory for Human Rights (SOHR) and the Local Co-ordination Committees (LCC), an opposition activist network, said the shelling killed at least one person on Sunday.
The SOHR urged the UN to intervene and evacuate more than 1,000 Homs families, including women and children. It says their lives are in danger.
The latest shelling comes a day after UN observers suspended their patrols in Syria due to a recent spike in violence.
About 300 observers are deployed in Syria, entrusted with monitoring a ceasefire and supporting the full implementation of a six-point peace plan drafted by UN-Arab League envoy Kofi Annan, which was supposed to lead to talks between the two sides.
However, hundreds of people have been killed since the first observers were deployed in April and the mission has been harshly criticised by the opposition.
Activists said that more than 50 people were killed on Saturday alone in clashes and shelling in towns close to Damascus, in the central provinces of Homs and Hama, in the seaside province of Latakia, the northern provinces of Idlib and Deir az Zour and the southern province of Daraa.
The mission's chief, General Major Robert Mood, has called for the evacuation of people from the city of Homs and other combat zones.
He said that neither Syrian troops nor opposition fighters were willing to hold their fire to allow them to leave, particularly from Homs.
In-depth coverage of escalating violence across Syria
"The parties must reconsider their position and allow women, children, the elderly and the injured to leave conflict zones without any preconditions and ensure their safety,'' Mood said in a statement on Sunday. "[UN] attempts to extract civilians from the line of fire over the past week have been unsuccessful".
"This requires willingness on both sides to respect and protect the human life of the Syrian people."
The suspension would be reviewed on a daily basis and operations would resume when the situation allowed, he said.
"The lack of willingness by the parties to seek a peaceful transition, and the push towards advancing military positions is increasing the losses on both sides: innocent civilians, men, women and children are being killed every day," Mood's statement said.
"It is also posing significant risks to our observers."
'Stop all violence'
Mood said intensifying violence in the past 10 days was "limiting our ability to observe, verify, report as well as assist in local dialogue and stability projects".
The National Co-ordination Committee (NCC), one of Syria's main opposition factions, expressed regret over the suspension and called for the supervision mission to strengthen its security apparatus and resume operations.
Mahmoud Morei, the NCC head, said the Syrian government should shoulder the majority of responsibility for the intensifying violence. He suggested that the government should first stop using violence because it has not resolved the problem over the past 10 months.
On the contrary, it had deepened the crisis, he said.
"We demand the Syrian authorities to stop all violence right away, even it is an unilateral ceasefire in order to seek a way out from the crisis," Morei said.
At the same time, the Syrian foreign ministry said it understood the UN mission's decision, noting that armed groups in Syria have stepped up assaults since the UN-led peace plan went into effect in April.
Activist say more than 14,000 people have been killed since the uprising against President Bashar al-Assad began in March 2011.