Battles in and around the Syrian city of Aleppo have killed at least 70 pro-government fighters and more than 80 insurgents after the army launched an offensive there, a monitoring group said on Wednesday, Reuters reported.
The army backed by allied militia had captured areas north of Aleppo on Tuesday in what the Syrian Observatory for Human Rights said was an attempt to encircle the northern city and cut off insurgent supply lines.
Aleppo is at the forefront of clashes between the army and a range of insurgents, including Islamist brigades, al Qaeda's Syria wing Nusra Front and Western-backed units battling President Bashar al-Assad.
The United Nations is seeking a ceasefire there, a step towards addressing the crisis in Syria which is about to enter its fifth year.
The advance on Aleppo is the second major offensive by pro-government forces in a week. The army and allied combatants from Lebanon's Hezbollah group have also launched a large-scale assault in southern Syria against insurgents.
On Wednesday the main route leading north out of Aleppo to the Turkish border was blocked and under fire by pro-government forces, the Observatory's founder Rami Abdulrahman said.
"The regime went forward a bit yesterday and the road is still closed," he said. The army was controlling the route from positions it set up in the villages of Bashkuwi and Sifat on Tuesday on either side of the road, he said.
Insurgents can take another route north but it entails going northwest out of the city and circumnavigating army-held areas before heading north again. "It is the very long way around," he said. He also said poor weather prevented Syrian air force bombardment on Wednesday but fighting continued on the ground.
Casualties on the government side could be higher because 25 of its combatants were unaccounted for, he said. Sixty-six Syrian insurgents from various groups were killed in the fighting, as well as at least 20 from Nusra Front, he said.
Around 60 Syrian soldiers reached the Shi'ite Muslim towns of al-Zahra and Nubl north of Aleppo after retreating from battles in the town of Ratain on Tuesday, the Observatory said.
Fighting had also raged in several Aleppo city districts on Tuesday. SANA, Syria's state news agency, said the army seized at least six villages near Aleppo on Tuesday.
On Tuesday United Nations Syria envoy Staffan de Mistura said the government was willing to suspend air strikes and shelling of Aleppo for six weeks so that a local ceasefire plan could be tested. But he played down prospects for wider progress.
"Every time there is a proposal of a ceasefire ... history has proven that there is some type of acceleration in order to take a better position," he said. "I fear that could be the case."
The Syrian conflict started in 2011 with protests against Assad and has descended into a civil war, drawing in foreign fighters on both sides.