Major players in Syria's war have traded accusations over violations of the first major truce in the five-year conflict, but the conditional ceasefire remains largely intact.
The main opposition grouping, the High Negotiations Committee (HNC), on Sunday described the ceasefire as "positive" but lodged a formal complaint with the UN and foreign governments about breaches on the first day.
Al Jazeera's Omar al-Saleh, reporting from the Turkish border town of Gaziantep, said the opposition had described the violence as a "violation of the terms of the ceasefire".
"Now the Russians are saying they targeted members of al-Nusra Front, which is linked to al-Qaeda and of course are excluded from the terms of this deal," he said.
The Islamic State of Iraq and the Levant (ISIL) group, which has seized territory in both Syria and Iraq, is also excluded from the deal.
The war in Syria has claimed 270,000 lives and displaced more than half the population.
Aid organisations hope to use the lull in fighting to deliver desperately needed supplies.
A successful truce would also create a more favourable backdrop for peace talks that collapsed in acrimony in early February as a Russia-backed government offensive in northern Syria caused tens of thousands to flee.
Referring to the humanitarian situation, our correspondent said: "We are told they [aid agencies] hope by tomorrow [Monday] to have another convoy to similar areas that received aid in previous days, but these are not in a dire situation like areas such as [the Damascus suburb of] Daraya, which has had no aid whatsoever."
"This is a logistical nightmare and you need a lot of paperwork to get into those areas."
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Salem al-Meslet, a spokesman for the HNC, said: "We have violations here and there, but in general it is a lot better than before and people are comfortable.
At the same time, an HNC letter to Ban Ki-moon, the UN secretary-general, accused Bashar al-Assad's government and its allies of committing "24 violations with artillery shelling and five ground operations ... in 26 areas held by the moderate opposition".
The letter, signed by HNC head Riad Hijab, also criticised Russia for conducting "26 air strikes on areas falling within the ceasefire".
Violations 'here and there'
Hijab said the ceasefire breaches had killed 29 people and wounded dozens.
The HNC says it has not receive any maps outlining which areas are included in the ceasefire or documents explaining the monitoring mechanism.
Syria's Al-Watan daily, which is close to the government, said on Sunday that those maps were still being "kept secret".
Separately, Saudi Arabia, a staunch opponent of Assad's government, accused Russia of flouting the ceasefire and targeting "moderate opposition" groups.
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"Things will become clearer in the coming days on whether the regime and Russia are serious or not about the ceasefire," Adel al-Jubeir, Saudi foreign minister, said.
For its part, Russia, which has waged a five-month bombing campaign to support Assad, blamed "moderate" rebels, Turkey and "jihadists" for nine ceasefire violations.
But "on the whole, the ceasefire regime in Syria is being implemented," Lieutenant-General Sergei Kuralenko, head of Russia's coordination centre in Syria, was quoted as saying by Russian news agencies.
The Syrian Observatory for Human Rights (SOHR), the Britain-based monitoring group, reported air strikes - believed to be either Syrian or Russian - on seven villages in Hama and Aleppo provinces.
It was unclear if the raids hit areas covered by the ceasefire, which excludes territory held by ISIL and al-Nusra Front.
Rami Abdurrahman, SOHR head, said only one of the villages, Kafr Hamra in Aleppo, is controlled by al-Nusra while the others are held by moderate rebels.
As recriminations resume, the US has urged everyone to be patient.
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"Setbacks are inevitable," a senior US administration official said.
"Even under the best of circumstances, we don't expect the violence to end immediately. In fact, we are certain that there will continue to be fighting, in part because of organisations like ISIL and al-Nusra."
A task force set up to monitor the deal described Saturday's first day as largely successful.
The UN reported "some incidents" in apparent violation of the truce, but "they have been defused", he said.
Staffan de Mistura, the UN's Syria envoy, aims to relaunch peace talks on March 7 if the ceasefire lasts and more aid is delivered.
Source: Al Jazeera and agencies