BEIRUT, Lebanon — Street protests erupted across insurgent-held areas of Syria on Friday, as demonstrators took advantage of the relative lull in airstrikes during a partial truce, coming out in the largest numbers in years to declare that even after five punishing years of war they still wanted political change.

Under the slogan “The Revolution Continues,” demonstrators waved the green, white and black pre-Baathist flag adopted during the early, largely peaceful stages of the revolt, before the proliferation of armed Islamist factions with black jihadist banners.

It was impossible to gauge what percentage of Syrians the demonstrators represented, out of the millions living in insurgent-held areas or, for that matter, in government-held areas or as refugees abroad. But many protesters, reached by telephone and text message, said they aimed to show that they were determined to resume demonstrations seeking the ouster of President Bashar al-Assad as soon as there was even a partial respite from airstrikes by the government and its Russian allies.

The protests were all the more surprising in that the insurgency is struggling militarily, squeezed between pro-government forces and those of the Islamic State.