Groups of Iranian troops have been arriving in Syria via an airport in Latakia province, activists and a monitoring group say, as the Syrian army launches a major offensive north of the strategic city of Homs.
More Iranian troops have arrived in Bassel al-Assad International Airport, near Jableh in Latakia province, the Syrian Observatory for Human Rights said on Thursday.
The Syrian government halted all flights in and out of the airport on Tuesday and the airport is currently being used by Russia and Iran as an airbase, the UK-based activists' network said.
Al Jazeera could not independently verify the reports of the Iranian deployment.
The airport has recently become a hub for Iranian and Russian forces, where activists confirmed to the Syrian Observatory that thousands of Iranian troops have arrived in the past few weeks in that airport.
Russian fighter jets also reportedly use the Bassel al-Assad International Airport, and, following a near miss in Syrian airspace, the US and Russia have held talks on flight safety.
The Iranians' reported arrival suggests that, for now, taking on the Islamic State of Iraq and the Levant (ISIL) group in eastern Syria seems a secondary priority to keeping President Bashar al-Assad in power.
The developments came a day after Alaeddin Boroujerdi, head of the Iranian parliament's National Security and Foreign Policy Commission, met the Syrian parliament speaker in Damascus to discuss the joint operation against opposition fighters in northwest Syria.
"If Syria makes a request [for Iranian forces], we will study the request and make a decision," Boroujerdi was quoted saying on Thursday by AFP.
"What's important is that Iran is serious about the fight against terrorism. We have supplied aid and weapons and sent advisers to Syria and Iraq."
He said "military operations" currently under way in Syria "take place in support of a political solution and peace" in the country, in an apparent reference to Russia's campaign.
Two Syrian officials told Reuters news agency the ground offensive would target opposition fighters in Aleppo.
The operation, which the officials said would be backed by Russian air strikes, underlined the growing involvement in the civil war of Syrian President Bashar al-Assad's two main allies, which has alarmed a US-led coalition opposed to him that is bombing ISIL.
The officials told Reuters Iran has sent thousands of troops into Syria in recent days to bolster the ground offensive in Aleppo.
On the ground, Syrian state television and the Syrian Observatory say, government forces and other pro-government groups, backed by Russian jets, have launched an attack on opposition-held towns north of the city of Homs.
The Russian air strikes hit targets around the town of Talbiseh, Rastan and the villages of Teir Malla, Dar Kabira and Khalidiya, a few miles north of the mainly government-held city, the Syrian Observatory said on Thursday.
It said government forces and fighters from Lebanon's Shia armed group Hezbollah were involved in the assault.
Activists told Al Jazeera that at least 14 civilians were killed in a the air strikes that targeted an internally displaced shelter in Teir Malla.
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Rami Abdel Rahman, the head of the Syrian Observatory, said six opposition fighters and at least four civilians had been killed.
The Sunni Muslim town of Talbiseh and the surrounding villages north of Homs are located in an enclave of opposition to Assad.
Hezbollah's Al Manar television channel said the Syrian army was carrying out a land offensive in northern Homs province.
A news flash on Syrian state TV said the army had begun a military operation in the north Homs countryside after "concentrated air strikes and heavy preparatory artillery shelling on the terrorist groupings and their bases".
Recapturing the area would help reassert Assad's control over the main population centres of western Syria and secure territory linking Damascus to the coastal heartland of his minority Alawite sect.
The Syrian army has launched several ground offensives to retake lost territory since Russian jets started air strikes against rebel targets mainly in western Syria two weeks ago.
Source: Al Jazeera and agencies