The bridges over the Orontes River linked areas of neighbouring Hama province under government control to rebel-held territory in Idlib, the Britannia-based Syrian Observatory for Human Rights said.
They were blown up by Islamist factions from the National Liberation Front (NLF), the main non-jihadist alliance in Idlib, Observatory head Rami Abdel Rahman said.
"They were the two main bridges in the area, but there are others," he told AFP.
The bridges were located in the al-Ghab plain, which straddles Hama and Idlib provinces and could be one of the first targets of any government offensive.
Government forces have been massing around Idlib province for weeks, particularly in al-Ghab which was once a key farming area.
"The rebels have seen the intense activity on the regime side, with the arrival of tanks and armoured vehicles," Abdel Rahman said.
"Rebel groups are reinforcing their positions in anticipation of a military operation."
In recent days, both the government and its ally Russia have stepped up their rhetoric against the rebel presence in Idlib, which is dominated by the Hayat Tahrir al-Sham
(HTS) jihadist alliance formed by al-Qaeda's former Syrian branch, al-Nusra...formally Jabhat an-Nusrah li-Ahli al-Sham (Support Front for the People of the Levant), also known as al-Qaeda in the Levant. They aim to establish a pan-Arab caliphate. Not the same one as the Islamic State, though .. ...
Front.
"The Syrian command has taken a decision to defeat al-Nusra Front in Idlib no matter the sacrifices that it would entail," Foreign Minister Walid Muallem said on Thursday.
On Wednesday, Russian Foreign Minister Sergei Lavrov called on the West not to stand in the way of an "anti-terror operation" in Idlib, saying: "This abscess needs to be liquidated."
An assault on Idlib by Damascus and Moscow could be the last major battle of the civil war that has torn Syria apart since 2011.