Hezbollah is fighting alongside government forces.
Syrian troops and allied militiamen entered the jihadist-held town of Albu Kamal on Wednesday, state media said, edging closer to ousting the Islamic State group from its last urban stronghold in the country.
According to Al-Abadi, Iraqi forces are now in control of oil refineries in the north.
"The advance towards Albu Kamal came after army troops and their allies met up with Iraqi forces at the border between the two countries", SANA said.
The battle for Al-Bukamal took on a potentially new dimension amid widely spread, yet unconfirmed reports suggested that the elusive ISIS chief Abu Bakr al-Baghdadi had recently fled to the town. "The CAOC [Combined Air Operation Center in Qatar] essentially controls our air forces in Syria, Iraq and Afghanistan and other areas, can easily flex our air power day by day to areas as required, and Afghanistan is an example of that".
Croft revealed that aircraft has yet to be moved out of Iraq and Syria.
First appearing as a major threat in Iraq and Syria in 2014, the Islamic State, also known as ISIS, are being driven out of the cities they previously occupied. In the years since, however, local and worldwide forces have reduced ISIS territory in both countries to a fraction of its former self.
The Iraqi Popular Mobilisation Forces (PMF), an alliance of militias, earlier on Wednesday denied it had crossed the Syrian border and was attacking Albu Kamal. Al-Abadi made his comments at a news conference following his weekly Cabinet meeting.
But the jihadist group has seen that territory shrink to a small pocket along the Euphrates River, with Albu Kamal as its final hub.