Rebel factions in Syria that backed recent peace moves say an intensification of government attacks has put the current truce in jeopardy.
They warn that they reserve the right to respond to recent bombings of areas around Damascus, Homs and the south.
The rebels describe the attacks as a "bloody message" from President Bashar al-Assad's government.
This comes just days before UN-sponsored talks are due to start in Geneva, Switzerland.
The UN envoy to Syria, Staffan de Mistura, has played down hopes for the talks on 23 February.
He said the talks were aimed at seeing if there was any possibility of starting to discuss a political process.
A nationwide ceasefire brokered by Russia, Turkey and Iran took effect on 30 December after peace talks in Kazakhstan.