Syrian military helicopters dropped thousands of leaflets over Damascus and its suburbs Tuesday, urging rebels to hand over their weapons or face "inevitable death."

The leaflets appear to be part of the regime's psychological warfare against the rebels, but are highly unlikely to have any effect on fighters intent on toppling President Bashar al-Assad's regime. Human rights groups say more than 20,000 people have been killed in Syria since the revolt against Assad began in March 2011.

For more than a month, the military has been fighting major battles against rebels in the outskirts of Damascus and its suburbs while engaged in what appears to be a stalemated fight in the north against rebels for control of Aleppo, the nation's largest city and commercial capital.

The government recently has intensified its offensive to recapture rebellious districts on the capital's periphery, and hundreds of people have been killed in several days of shelling and clashes in the affected areas. Over the weekend evidence mounted of mass killings by regime forces in the Damascus suburb of Daraya after it was stormed by troops.

Some of the leaflets dropped Tuesday, which were signed by the armed forces and the army's general command, read: "The Syrian army is determined to cleanse every inch in Syria and you have only two choices: Abandon your weapons ... or face inevitable death."

"No one will help you. They have implicated you in taking up arms against your compatriots," they said. "They drown in their pleasures while you face death. Why? And for whom?"

Syrian authorities blame the 17-month uprising on a foreign conspiracy and accuse oil-rich Gulf countries Saudi Arabia and Qatar, in addition to the U.S. and Turkey, of backing "terrorists" seeking to oust the regime.

Assad told an Iranian delegation this week that he was determined to crush the conspiracy against Syria "whatever the price."

With its forces stretched thin by fighting on multiple fronts, Assad's regime has increasingly turned to air power, unleashing both helicopters and fighter jets on the rebels.

The lightly armed fighters, in turn, have grown bolder and their tactics more sophisticated in recent months. Rebels claimed to have shot down a military helicopter that crashed in flames in the Damascus district of al-Qaboun Monday. State media confirmed the crash but gave no details about the cause.