 LONDON -- The cease-fire in eastern Aleppo was broken today and the planned evacuation of civilians has stalled, opposition sources and residents said.

Iran and Russia disagreed on the terms of the agreement and evacuations have been postponed until Thursday, the sources said.

“Iran and the government refused the agreement,” Brita Hagi Hassan, president of the city council for opposition-held Aleppo, told ABC News. “After the wounded were ready to be evacuated, Iran and the government refused to get them out.”

TV footage this morning showed green buses in Aleppo ready and waiting.

Artillery shells have reportedly been fired on eastern Aleppo neighborhoods since the morning, breaking the truce that came into effect Tuesday night.

“The agreement has been broken,” Mohammad Abu Rajab, a radiologist in eastern Aleppo, told ABC News. “No one can even walk in the streets. Hundreds of rockets and shells fell on us. Please let us stay alive and out safely.”

There were no ambulances, he added, and the wounded are bleeding to death in the streets.

This comes after Russia Tuesday announced that the Syrian government had gained full control of eastern Aleppo and that fighting had stopped.

"The Syrian government has re-established control over eastern Aleppo," Vitaly Churkin, Russia’s United Nations ambassador, told the U.N. Security Council Tuesday.

After his statement, residents of eastern Aleppo said it was quiet there. It remained quiet overnight until the truce was broken this morning, they said.

The Russian announcement came after months of siege and years of fighting between rebels and Syrian government forces. In recent months, the Syrian government, with help from its Russian and Iranian allies, intensified its airstrikes on eastern Aleppo and tightened the siege in an attempt to gain full control of the area, which was held by rebels until recently.

By Tuesday morning, the Syrian government had taken over the city except for a small and shrinking enclave in the eastern part of the city. Gaining control of the eastern neighborhoods is a strategic victory for President Bashar al-Assad.