Iranian guard
Iranian soldiers march during the annual military parade marking the anniversary of the start of Iran's 1980-88 war with Iraq, Sept. 22, 2015, in the capital Tehran. Iran reportedly is pulling back troops in Syria. ATTA KENARE/AFP/Getty Images

Iran has pulled out some of its elite fighters from the Russian-led military campaign in Syria, Western military officials told Bloomberg News. The apparent retreat comes as some high-level Iranian officers have been killed and wounded in a campaign meant to help bolster the Syrian government by retaking key areas captured by Western-backed opposition forces, including Idlib Province.

"They are losing lieutenants," Robert Ford, a former U.S. ambassador to Syria, told Bloomberg. "When you lose lieutenants it means you are losing people fighting on the front lines."

Iran has reportedly lost more than 100 of its fighters, including top generals. Some said the apparent retreat was simply a change in military strategy.

Russia initially began its campaign in Syria in September with a plan to drive rebels out of Idlib and other cities within three months, Israeli Defense Minister Moshe Ya’alon said at the Saban Forum at the Brookings Institution Friday. "It’s not going to happen because of the military difficulties," he said, adding the campaign appears to have failed. Early on, the campaign was criticized for its targeting of anti-regime rebels, many backed by the West and Gulf states, rather than focusing on weakening the Islamic State group. Rights organizations also said the Russian-led campaign was targeting civilian infrastructure.

The Wall Street Journal reported there were some 7,000 Iranian Revolutionary Guard Corps soldiers and other militia volunteers in October. That number has since dwindled, with now as few as 700 Revolutionary Guard Corps members, according to an estimate by a senior Western defense official cited by Bloomberg. While International Business Times could not independently verify the purported Iranian retreat, the move could signify a shift in Iran’s role in the civil war in Syria. However, Iranian leaders have continued to demand Syrian President Bashar Assad remain in power.

A top adviser to Iran’s supreme leader said earlier this week Assad's future could be determined only by the Syrian people and that foreign intervention was a “red line” for Tehran. His fate has been a sticking point in talks among world leaders to bring about an end to the violence in Syria.