The truce in Syria is mostly holding despite of violations including war planes attacking six towns in the northern Aleppo province early on Sunday, the Syrian Observatory for Human Rights said, a day after a cessation of hostilities agreement took effect.The Syrian opposition said Bashar al-Assad's regime and its allies of breaching the truce 15 times Saturday but said on Sunday that it will stick to the cessation of hostilities.A spokesman for the High National Committee (HNC) said: "Yesterday was the first day people can really go out and walk in the streets."But he said HNC will send letters to U.N. and foreign ministers to complain about the Russian airstrikes around Aleppo and attacks by Hezbollah in Zabadani.The spokesman also said HNC has asked the U.S. for information about how monitoring of truce works but has yet to receive any answer.He said the violations included shelling in the province of Latakia.Meanwhile, Saudi Foreign Minister Adel al-Jubeir also said Assad forces are violating the cease-fire brokered by Russia and the U.S. Speaking to reporters in the Saudi capital Riyadh on Sunday during a press conference, Al-Jubeir said "there are violations to the ceasefire from Russian and (Syrian) regime aircraft,"The foreign minister reiterated Saudi Arabia's position that Assad has no place in the future of Syria and that he must leave power, either peacefully or through military means.Earlier, the Observatory which monitors the conflict said the identity of the jets was not clear"We do not know which planes carried out the strikes and also we are not sure if this is considered a breach to the truce because it is not clear if these towns are included in the truce," the Observatory's director Rami Abdulrahman said.Syria's state media did not mention the strikes. Russia's defence ministry declined to comment.Abdulrahman said some of the towns which were attacked, including Daret Azza, were controlled by the Nusra Front and other groups.Other attacks hit the villages and towns of Qabtan al-Jabal, Andan, Hreitan, Kfar Hamra and Ma'aret al-Arteek, the Observatory said, all in the west of the province where insurgents from the Free Syrian Army, who are covered by the truce, have operated.Two videos sent by an opposition commander to Reuters shows a strike in another town, Harbnafseh, at 6.30 a.m. (0430 GMT) and another at 07:00 a.m. (0500 GMT) according to the voice in the video. The footage shows plumes of smoke rising into the sky.Under the U.S.-Russian accord accepted by Bashar al-Assad's government and many of his foes, fighting should cease so aid can reach civilians and talks can open to end a war that has killed more than 250,000 people and made 11 million homeless.Russia, which says it intends to continue strikes against areas held by fighters that are not covered by the truce, said it would suspend all flights over Syria for the first day to ensure no wrong targets were hit by mistake.The truce seemed largely to be holding, though opposition fighters reported what they described as occasional government violations, and one commander warned that unchecked, the breaches could lead to the agreement's collapse.Jaish al-Nasr, a group affiliated to the Free Syrian Army (FSA) which has backed the truce, said government forces had fired mortars, rockets and machine guns in Hama province and that warplanes had been constantly present in the sky."Compared to the previous days it is nothing, but we consider that they broke the truce," Mohamed Rasheed, head of the group's media office, told Reuters.Another FSA-affiliated group, Alwiyat Seif al Sham, said two of its fighters had been killed and four more wounded when government tanks shelled them in rural areas west of Damascus.A Syrian military source denied the army was violating the truce agreement. State media described rocket attacks near Damascus and several deadly attacks by Daesh. But overall the level of violence was far reduced."Let's pray that this works because frankly this is the best opportunity we can imagine the Syrian people has had for the last five years in order to see something better and hopefully something related to peace," U.N. Syria envoy Staffan de Mistura said at a midnight news conference in Geneva."I think that the feeling that we have today is that the situation is very different but of course every day has to be monitored," he said.The agreement is the first of its kind to be attempted in four years and, if it holds, would be the most successful truce of the war so far.De Mistura said he intends to restart peace talks on March 7, provided the halt in fighting largely holds.But there are weak spots in a fragile deal which has not been directly signed by the Syrian warring parties and is less binding than a formal ceasefire.The truce is the culmination of new diplomatic efforts that reflect a battlefield dramatically changed since Russia joined the war in September with airstrikes to prop up Assad. Moscow's intervention effectively destroyed the hope his enemies have maintained for five years -- encouraged by Arab and Western states -- to topple him by force.Like several other opposition figures contacted by Reuters, Fares Bayoush, head of the Fursan al-Haqq opposition group which fights under the FSA banner, said front lines were far quieter. But he added that violations were taking place and if continued could lead to the "collapse of the agreement".In early reports of violence, a Syrian opposition group in the northwest said three of its fighters had been killed while repelling an attack from government ground forces a few hours after the plan came into effect.Syria's state media said at least six people were killed and several wounded in two suicide bomb attacks east of Hama city, including the car bomb claimed by Daesh. Three children were killed and 12 wounded in an unspecified Daesh attack in Joura neighborhood in Deir al-Zor province.Fadi Ahmad, spokesman for the FSA First Coastal Division in Latakia province said government helicopters had dropped eight "barrel bombs" on the area in the early afternoon. Assad's opponents have long accused the government of using such bombs -- oil drums packed with explosives -- to cause indiscriminate damage in opposition-held areas, which Damascus denies.The Syrian Observatory for Human Rights, a monitoring group, said government forces dropped five barrel bombs on the village on Najiya in Idlib province. The village is controlled by several groups including the Nusra Front.