AMMAN, Aug 26 (Reuters) - Fifty rebels and their families were evacuated on Thursday from the last opposition bastion in southern Syria under a Russian-sponsored deal to avert a military showdown in the strategic border area with Jordan and Israel, witnesses, rebels and army sources said. A contingent of Russian military police on Tuesday entered the enclave to impose a plan that allows the army to take it over, while offering safe passage to former rebels who oppose the deal to leave for opposition areas in northwest Syria. The Russian move halted an attempt to storm the enclave by pro-Iranian army units led by the elite Fourth Division who hold sway in the region and had in recent days tightened a two-month siege, escalating shelling and pushing for a military offensive. The Syrian army, aided by Russian air power and Iranian militias, in 2018 retook control of the province of which Deraa is the capital and which borders Jordan and Israel"s Golan Heights. That deal forced thousands of mainstream Western-backed rebels to hand over heavy weapons but kept the army from entering the bastion known as Deraa al Balaad. However, Moscow gave guarantees to Israel and Washington in 2018 that it would hold back Iranian-backed militias from expanding their influence in the strategic region. U.S. Secretary of State Antony Blinken had earlier this month condemned what he termed the "Assad regime"s brutal" assault on Deraa and called for an immediate end to violence "that killed civilians and displaced thousands." Over 50,000 civilians along with several thousand former rebels lived in the stronghold that was the site of the first peaceful protests against the Assad family rule, which were met by force before spreading across the country. The area has now become a ghost town after weeks of intermittent fighting and shelling during which the army has prevented food, medical and fuel supplies coming in but opened a corridor for civilians to leave, residents and local officials say. The enclave and other towns in southern Syria have, since the state regained control of the province, held sporadic protests against President Bashar al Assad"s authoritarian rule that are rare in areas under state control.