Syria crisis: UN 'must stop flagrant violation of humanitarian law'
UN humanitarian chief Valerie Amos has urged the Security Council to act immediately to ensure more humanitarian access in war-torn Syria.
She said it was "unacceptable" that both Damascus and rebels continued to "flagrantly" violate humanitarian law.
The council has been deadlocked over aid deliveries in Syria, where millions have been forced to flee their homes.
Peace talks between the government of President Bashar al-Assad and Syrian opposition groups remain deadlocked.
The UN-Arab League envoy to Syria, Lakhdar Brahimi, says he has been reassured by US and Russian officials that they would try to "unblock the situation".
But Russian Foreign Minister Sergei Lavrov said on Friday that Moscow had "an impression" that there were attempts to derail the Geneva talks.
Without naming anyone, Mr Lavrov said that those who supported the opposition "in fact had in mind one thing only - regime change".
"Everything they want to talk about is the creation of a transitional governing body," he said.
The UN human rights office has warned about a big build-up of government forces around the city of Yabroud, which is being hit by air strikes.
The UN refugee agency says it is preparing for an influx of refugees out of Yabroud across the border into Lebanon.
The town is the last rebel stronghold in the Qalamoun mountains, near the Lebanese border.
There has been a surge in fighting across Syria in recent weeks, with both sides apparently trying to gain territory to strengthen their hands in the talks.
Briefing the UN Security Council on Thursday, Baroness Amos said: "It is unacceptable that four months since the members of that Council demanded action, international humanitarian law continues to be consistently and flagrantly violated by all parties to the conflict.
"All parties are failing in their responsibility to protect civilians. We understand that a war is going on, but even wars have rules."
Speaking to the BBC's Nick Bryant, Baroness Amos said a UN-brokered ceasefire deal which has allowed civilians to be evacuated from the besieged Old City of Homs in the past few days did not offer a long-term solution.
"It's 14 months since I raised the alarm in the Security Council about Homs. We managed to get 1,200 people out of Homs, we managed to get food and medicines in for 2,500 people," she said.
"If it's going to take 14 months to do that when you've got 250,000 people in besieged communities, when you've got over three million people in hard-to-reach communities, I really find it very difficult to say that this is a [right] model."
The Security Council remains deadlocked over the issue.
The US, Britain and France favour a toughly-worded resolution, but it is opposed by Russia which has put forward an alternative draft on fighting what it calls "terrorism" in Syria and offering its own plan for improving aid, our correspondent adds.
The civil conflict in Syria has claimed more than 100,000 lives since March 2011. Some 9.5 million people have been forced to flee their homes.