Syrian opposition fighters have taken control of Maarat al-Numan, a strategic town in Idlib province on the highway linking Damascus with the commercial hub of Aleppo, activists say.
"Regular forces pulled back from all of their checkpoints around Maarat al-Numan, except for one at the entrance of the town," Rami Abdel Rahman, a UK-based activist who gets information from a network of sources on the ground in Syria, said on Tuesday.
"This is a strategic location on the route from Damascus to Aleppo. All the regime reinforcements headed to Aleppo must pass through Maarat al-Numan.
Rebels forces were holding all but one of the town's checkpoints and residents were fleeing the area and surrounding villages because of intense shelling, an Al Jazeera report in Maarat al-Numan said.
In a video released by activists on Tuesday, about 20 fighters belonging to the Martyrs' Brigade could be seen gathered around a tank at a captured army checkpoint in Maarat al-Numan shooting into the air in celebration.
"This is your tank, O Bashar!" they cried out in reference to President Bashar al-Assad. Maarat al-Numan had originally fallen under rebel control on June 10, but it was retaken by the army in August.
Joshua Landis, director of the Centre for Middle East Studies at Oklahoma University, told Al Jazeera that Maarat al-Numan would represent an important win.
"It's one of the key provincial cities in this greater Idlib area that's south of the Turkish border, and it's been fought over for months," said Landis.
"We've seen the rebels, in the last month, have advanced into Aleppo, but the battle has been very dreary in Aleppo and much of the city has been destroyed."
Landis added that the opposition fighters have not yet "been able to convincingly defeat the Syrian army there".
Tuesday's reported rebel advance came after 48 hours of fierce fighting and army bombardments.
Al Jazeera is unable to independently verify reports of violence, as the Syrian government has placed strict restrictions on reporting, although our correspondent in Syria confirmed that warplanes bombed Maarat al-Numan.
Elsewhere in the country, soldiers moved into the central city of Homs and Reuters news agency reported that rebel suicide bombers struck at an Air Force Intelligence compound in Damascus used as an interrogation centre - the latest attack to bring the conflict close to Assad's power base.
Tension with Turkey
Meanwhile, NATO said it had drawn up plans to defend Turkey if necessary should the war in Syria spill over their border again, a week after five Turks were killed when mortars fired from Syria landed in a border town.
Fighting between Syrian rebels and government forces could be heard from the Turkish border on Tuesday following several days of clashes on the Syrian side.
In-depth coverage of escalating violence across Syria
"Assad...is only able to stand up with crutches," Turkish Prime Minister Recep Tayyip Erdogan told a meeting of his ruling AK Party.
"He will be finished when the crutches fall away."
Erdogan, reacting to six consecutive days when shells fired from Syrian soil have landed on Turkish territory, has warned Ankara will not shrink from war if forced to act.
But his government has also stressed it would be reluctant to mount any big operation on Syrian soil and then only with international support.
It was not clear whether the shells hitting Turkish territory were aimed to strike there or were due to Syrian troops overshooting as they attacked rebels to their north.
NATO Secretary-General Anders Fogh Rasmussen said in Brussels the 28-member military alliance hoped a way could be found to stop tensions escalating on the border.
"We have all necessary plans in place to protect and defend Turkey if necessary," he said.