AMMAN, Aug 31 (Reuters) – Syrian elite forces aided by pro-Iranian militias stepped up an offensive on Tuesday against a rebel enclave in a southwestern pocket bordering Jordan and Israel, according to residents, military and opposition sources. Witnesses and military sources said dozens of improvised missiles were fired into Deraa al-Balaad by the Syrian military’s pro-Iranian Fourth Division, which is backed by Iranian-financed local militias. A halt to fighting was announced after Russian generals offered a new plan that appeared to meet some of the rebel demands to involve the Russian military police in patrolling the enclave while allowing for the first time a Syrian army security presence in the stronghold. The Syrian army said at least four soldiers were killed in ambushes on troops in the towns of Sanameen and Nawa, and that rebel shelling had caused several casualties in residential areas. Pro-Assad forces have prevented food, medical and fuel supplies from reaching Deraa al-Balaad but have opened a corridor for civilians to leave, according to local officials and residents.