Iran has sent around 1,500 fighters to Syria over the past few days, a regional official and Syrian activists claim.

The Iranian soldiers, bolstered by Russia’s airstrike campaign, are preparing for a grand offensive against militants in the northern Aleppo province, which would be announced in the coming days, the official told the AP. They’re also accompanied by a new wave of Hezbollah fighters.

The soldiers were arriving at Damascus airport and transported to a military base in the coastal town of Latakia.

The presence of Iranian troops could strengthen Russia's mission of empowering Syrian President Bashar Assad's embattled government.

"Sending more troops from Hezbollah, and Iran only increases the shelf life of the Syrian regime, which is destined to end," Maj. Jamil Saleh, the leader of Tajammu Alezzah, a CIA-backed Free Syrian Army faction, told the AP. "It will only add more destruction and displacement."

Their arrival is almost certain to fuel a civil war in Syria which has already claimed the lives of more than 250,000 people and displaced half of the country's population.

Iranian and Syrian officials have long claimed Iran has advisers and military experts in Syria. But Wednesday's reports are the first confirmation of Iranian fighters actually taking part in combat operations there.

Their arrival is almost certain to fuel a civil war in Syria which has already claimed the lives of more than 250,000 people and displaced half of the country's population. It also highlights the far-reaching goals of Russia's military involvement in Syria.

Meantime, an Iranian top parliamentarian says his country's cooperation with Russia, Syria and Iraq have proved "successful" in fighting terrorism in the region, the AP reports.

Alaeddin Boroujerdi, chairman of the National Security and Foreign Policy Committee of Iran's parliament, is set to convene with Syrian officials in Damascus on Wednesday.

Boroujerdi added the U.S.-led anti-terrorism coalition has failed to achieve results, opening the way for a more successful intervention.

The U.S. suspended its faltering rebel training program in Syria last week. It’s since shifted its strategy to equipping established groups to battle ISIS.

While the Russian intervention is supported by Iran, it has come under fire from NATO, which is discussing diplomatic responses to the conflict.

NATO has accused Russia of striking positions of rebel groups supported by the West and other regional players, and activists claim it has killed civilians and targeted historic Syrian sites, including the ruins at Palmyra.

Russia began its airstrike campaign in Syria on Sept. 30, and Syrian troops and allied militiamen began a ground offensive a week later.

The Associated Press contributed to this report.