By Lisa Barrington and Tom Miles
BEIRUT/GENEVA (Reuters) - A new ceasefire in Syria brought a full day with no combat deaths in the war between President Bashar al-Assad and his opponents, a monitoring body said on Tuesday, as efforts to deliver aid to besieged areas got cautiously under way.
Twenty-four hours after the truce took effect, United Nations Special Envoy for Syria Staffan de Mistura declared the situation had improved dramatically, saying U.N. aid access should be possible soon including to eastern Aleppo, the rebel-held half of the city that is under blockade.
The Syrian Observatory for Human Rights said it had not received a single report of combatants or civilians killed by fighting in any areas covered by the truce.
The ceasefire, brokered by the United States and Russia, is supported by countries that back Assad and his opponents, and marks the second attempt this year to halt a war that has frustrated peace efforts since fighting began more than five years ago.
The Observatory estimates the death toll since the start of the conflict at abound 430,000, in line with U.N. estimates. About 11 million people have been made homeless in the world's worst refugee crisis.
The ceasefire marks the biggest bet yet by Washington that it can work with Moscow to end a war that President Vladimir Putin transformed a year ago when he sent warplanes to join the fight on Assad's side.
Moscow and Washington have agreed to share targeting information for strikes against fighters from Islamic State and the former Syrian branch of al Qaeda, the first time the Cold War foes have fought together since World War Two.
The Observatory said the most intense fighting since the ceasefire began took place on Tuesday night in the village of Maan in Hama province. Insurgents operating in the Hama area included jihadists and nationalist rebels fighting under the Free Syrian Army banner.
It was not immediately clear if the rebels involved in the fighting were parties to the ceasefire.
A Syrian military source said armed groups had broken the ceasefire at 6 p.m. (10.00 a.m. ET) in Maan, attacking army positions with machine guns. Observatory Director Rami Abdulrahman said the fighting could be a serious threat to the ceasefire if it did not stop.
A senior State Department official clarified that all groups except Nusra Front, which has renamed itself Jabhat Fateh al-Sham, and Islamic State had to abide by the agreement.
"Our current understanding is that the only groups that are eligible to be targeted during this period are ISIS and al-Nusra Front," the official told a conference call with reporters.
Outside the scope of the truce, Turkey said on Tuesday that air strikes by a U.S.-led coalition had killed three fighters from Islamic State.
The agreement has been accepted by Assad and, far more reluctantly, by most of the groups that oppose him.
The international community's first goal is to deliver aid to civilians in Aleppo, Syria's biggest city before the war, which has been divided for years and where the opposition area is under siege.
In Geneva, de Mistura said there had been allegations of sporadic and geographically isolated incidents.
But he told reporters: "There is no doubt a significant drop in violence." While stressing that only 24 hours of relative calm had passed, he said: "Sources on the ground, which do matter, including inside Aleppo city, said the situation has dramatically improved with no air strikes."
While U.N. convoys have yet to enter Syria, de Mistura said that if the truce sticks, "(aid) access should be taking place very, very soon", and that the people of Syria could look forward to "no bombs and more trucks".
But he said the United Nations was still waiting for Damascus to issue letters authorizing the deliveries. "We are eagerly hoping and expecting the government to issue them very soon."
Syrian state media said armed groups had violated the truce in a number of locations in Aleppo city and in the west Homs countryside on at least seven occasions on Tuesday.
The Observatory said pro-government forces shelled near two villages in the south Aleppo countryside and a neighborhood on the outskirts of Damascus.
But the reports of violence were far less intense than normal. The Russian military, which sent reconnaissance equipment to detect and suppress attempts at violations, said the ceasefire had largely been observed in Aleppo.
Two aid convoys, each of around 20 trucks, crossed into northern Syria from the Turkish border town of Cilvegozu, about 40 km (25 miles) west of Aleppo, a Reuters witness said, although with security a concern, it was not clear how far into Syria they would go. A Turkish official said they carried mostly food and flour.
The Syrian government has said it would reject any aid deliveries to Aleppo not coordinated through itself and the United Nations, particularly from Turkey.
A second senior U.S. official said there were some "technical issues" to be resolved before the trucks could proceed.
"The regime is still present on the road, and under our agreement at some point in coming days they should be pulling back," the official told reporters. "The U.N. wants to make sure their convoys can get through both unhindered in terms of the regime and unthreatened in terms of the opposition, and to get safely into eastern Aleppo."
The head of the city council for opposition-held Aleppo expressed concern that planned deliveries would be conducted according to Russian wishes and not meet the needs of an estimated 300,000 people living there. Brita Hagi Hassan said the rebel-held part of the city was in dire need of fuel, flour, wheat, baby milk, and medicines.
Israel said its aircraft attacked a Syrian army position after a stray mortar bomb struck the Israeli-controlled Golan Heights, a now-routine Israeli response to the occasional spillover from the war. It denied a Syrian statement that a warplane and drone were shot down.
(Additional reporting by Lesley Wroughton in Washington, Tom Miles in Geneva, Yesim Dikmen in Istanbul, Tom Perry in Beirut, Jeffrey Heller in Jerusalem, Maria Kiselyova and Vladimir Soldatkin in Moscow and Orhan Coskun in Ankara; Writing by Nick Tattersall and Peter Graff; Editing by James Dalgleish and Peter Cooney)