The Syrian government has approved access to seven besieged areas and UN convoys are expected to travel to them within days, the United Nations said after crisis talks in Damascus.
UN Special Envoy Staffan de Mistura, who was given the green light at talks with Syria's Foreign Minister Walid al-Muallem, said on Tuesday that the UN would test the government commitment to allow access on Wednesday but gave no further details.
OPINION: Starving Syria as a weapon
Their meeting in Damascus came at a time when government forces had been advancing rapidly with the aid of Russian air strikes, and just days before an internationally agreed pause in fighting was due to take effect.
De Mistura said they had discussed the issue of humanitarian access to areas besieged by all sides in the five-year war.
"It is clear it is the duty of the government of Syria to want to reach every Syrian person wherever they are, and allow the UN to bring humanitarian aid," de Mistura said in a statement. "Tomorrow we test this."
'Degradation on ground'
The UN Office for the Coordination of Humanitarian Affairs (OCHA) said that Syria had approved access to Deir al-Zor; Fouaa and Kafraya in Idlib; and Madaya, Zabadani, Kafr Batna and Mouadamiya al-Sham in rural Damascus.
"Humanitarian agencies and partners are preparing convoys for these areas, to depart as soon as possible in the coming days," OCHA said.
It was not immediately clear whether the convoys would begin on Wednesday, as de Mistura had indicated.
Nor was there any indication of a breakthrough on access to areas besieged by armed opposition groups.
READ MORE: Nearly 400,000 Syrians starving in besieged areas
UN-backed peace talks are scheduled to resume in Geneva on February 25, after de Mistura suspended a first round earlier this month.
Last Friday, global powers meeting in Munich agreed to a pause in the fighting in the hope that this could allow the talks to resume, but the deal does not take effect until the end of this week and was not signed by all of Syria's warring parties.
"We are witnessing a degradation on the ground that cannot wait," UN spokesman Ahmad Fawzi told a news conference.
"The reason (de Mistura) suspended (the talks) was, as you know, that cities were still being bombed, people were still being starved on the ground."
Elsewhere, Russia denied bombing hospitals in northern Syria, with Kremlin spokesman Dmitry Peskov calling such accusations "unsubstantiated".
The rejection on Tuesday followed claims by France and Turkey that the bombing of two schools and five hospitals in Syria were "war crimes".
"Once again, we categorically reject and do not accept such statements," Peskov said when asked whether Russian planes bombed hospitals in Syria, including one supported by Doctors Without Borders (MSF).
"Especially since every time, those who make such statements are unable to prove in any way their unsubstantiated accusations."
READ MORE: Strikes on schools and hospitals in Syria 'war crimes'
The Kremlin spokesman added that Moscow preferred to rely on "first-hand sources" of information, which he said in this case would be the Syrian government.
Syria's ambassador to Russia, Riad Haddad, on Monday accused the US of bombing the MSF hospital and said that "Russian warplanes had nothing to do with any of it."
Strikes on hospitals in Idlib and Azaz killed almost 50 civilians including children, according to the United Nations, with UN Secretary-General Ban Ki-moon saying the raids violated international law and undermined efforts to end the five-year conflict.
The MSF confirmed its hospital was hit, without assigning blame. On Tuesday, MSF said the number of people killed in the air strike had risen to at least 11.
OPINION: Predicting Turkey's next move in Syria
The Syrian Observatory for Human Rights, a monitoring group based in the UK, said it suspected the Russian military was behind the attack, based on the location of the raids and the flight patterns and types of planes involved.
Turkish Prime Minister Ahmet Davutoglu on Tuesday denounced "vile, cruel and barbaric planes" of the Russian air force, saying they bomb "without discrimination between civilians and soldiers".
Russia's defence ministry, however, hit back with accusations that Turkey was shelling Syrian government forces from across the border.
"Since the end of last week Turkey is hitting Syrian government forces and patriotic opposition in border areas with large calibre artillery," spokesman Igor Konashenkov said in an emailed statement.