The statement from Free Syrian Army (FSA) chief Colonel Riad al-Asaad will deal a further blow to a ragged UN-backed ceasefire agreement that both sides are accused of disregarding.
"We will not stand with folded arms because we are not able to tolerate and wait while killings, arrests and shelling continue despite the presence of the (United Nations)observers who have turned into false witnesses," Asaad said, according to the London-based Asharq al-Awsat newspaper.
"Our people are also demanding we defend them in the absence of any serious steps by the Security Council which is giving the regime a chance to commit more crimes," he added.
The UN Security Council unanimously adopted a Russian-European drafted resolution last month that authorised an initial deployment of up to 300 unarmed military observers to Syria for three months, to be known as UNSMIS.
But despite an initial pause in fighting on April 12, a promised ceasefire has not taken hold. Nor has the carnage in Syria stopped, despite a parliamentary poll on Monday which the government promoted as a milestone on its path to reform but the opposition dismissed as a sham and boycotted.
International mediator Kofi Annan called on both Syrian government forces and opposition fighters to put down their weapons and work with the unarmed observers to consolidate the fragile ceasefire that took effect in April.
The newspaper quoted Asaad as saying the Free Syrian Army had devised a new strategy to make its attacks more effective.
Asked if his new strategy focused on bombings and targeting Syrian government security centres, Asaad said:
"Bombings are not part of our ethics and we don't need them. Our aim is to target military vehicles and we only use explosive devises."
The armed Syrian opposition is highly fragmented and there are militants groups in the country who say they do not take orders from Asaad. There has been a recent spate of bombings targeting Syrian security forces.
Asaad said the FSA had pulled out of cities to give the Annan plan a chance to succeed.
"The Free Syrian Army is still on the ground in most Syrian territories, and its departure from the cities was to spare civilians military operations and in order not to give the regime an excuse to say that we do not want a ceasefire," he added.