The fighting between Ahrar al-Sham, which is backed by Saudi Arabia, Qatar and Turkey, and al-Qaeda-linked Hay'at Tahrir al-Sham is the the first major escalation of infighting among Takfiri groups since they reached a truce in February.
Idlib has become the base for thousands of terrorists who fled Syria's largest city of Aleppo after facing a rout against government forces in December in their worst defeat since March 2011.
Rival terrorist groups are now competing for clout in the territories they control after seeing their campaign to topple the Syrian government broadly in tatters.
On Saturday, Ahrar al-Sham said Hay'at Tahrir al-Sham, also known as HTS, was sending reinforcements to the town of Saraqeb and the Jabal al-Zawiya region in preparation for an attack, accusing the group of acts of "tyranny."
The Ibaa News Agency of HTS, instead, accused Ahrar al-Sham of setting up checkpoints and detaining one of its commanders and his bodyguard.
The so-called Syrian Observatory for Human Rights, a UK-based monitor which is sympathetic to militants, said the two groups had clashed near the village of Tel Touqan.
More clashes loom as the two sides are rushing their fighters to the frontlines, with the US news agency Associated Press expressing worries that the infighting could affect their fight against Syrian forces who have been gaining ground over the past year.
Further confrontation could also draw other terrorist groups into the infighting, especially after Hay'at Tahrir al-Sham reported the deaths of two more members near the Sarjeh village and blamed Suqour al-Sham, a strong Ahrar al-Sham ally.
Hay'at Tahrir al-Sham is part of a Takfiri coalition spearheaded by Jabhat Fateh al-Sham, which was formerly known as al-Nusra Front or al-Qaeda’s Syria offshoot.
Due to the barbarity of their actions, al-Nusra and Daesh are not subject to an all-Syria truce deal clinched late last year with the mediation of Russia, Iran and Turkey.
The infighting among terrorist groups comes as international efforts to bring more Syrian areas under the ceasefire gain track and more militant groups desist from their campaign to topple the Syrian government.
On Saturday, Russia's Ambassador to the UN Office in Geneva, Alexey Borodavkin, said UN-led Syria talks have a chance of making progress because demands for the overthrow of President Bashar al-Assad have receded.
He said the seventh round of talks which ended on Friday had produced positive results, especially a "correction" in the approach of the main opposition delegation, the Saudi-backed High Negotiations Committee, whose mantra before was "Assad must go".
"The essence of this correction is that during this round the opposition never once demanded the immediate resignation of President Bashar al-Assad and the legitimate Syrian government."
Borodavkin said the HNC and its backers in Western and Persian Gulf capitals have realized that peace needs to come first, and then political reforms could be negotiated.
Over the past year, the opposition has suffered military defeats at the hands of Syrian forces and neither US President Donald Trump nor French President Emmanuel Macron is calling for Assad's immediate ouster.