TEHRAN, Iran (AP) — The Latest on Syria talks in Iran (all times local):

3:40 p.m.

The presidents of Iran, Russia and Turkey have begun a summit on Syria as a bloody offensive on Idlib province looms, despite warnings from the U.S. and others not to launch the attack.

The summit Friday between Iranian President Hassan Rouhani, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan may determine whether diplomacy halts any military action ahead of an anticipated offensive targeting the northwestern Syrian province.

Idlib province and surrounding areas are home to about 3 million people — nearly half of them civilians displaced from other parts of Syria. That also includes an estimated 10,000 hard-core fighters, including al-Qaida-linked militants.

Iran, Russia and Turkey all have their own competing interests over Syria. All also face U.S. sanctions under the administration of President Donald Trump.

____

3:30 p.m.

Residents in Syria's northwestern Idlib province are holding mass rallies in the rebels' last bastion, protesting an imminent government offensive there and chanting against the country's ruler President Bashar Assad.

The Friday rallies came as Presidents of Iran, Turkey and Russia are meeting in Tehran to discuss the war in Syria. The summit may determine whether diplomacy halts any military action in Idlib and its surrounding areas, home to more than 3 million people. Nearly half of the area's residents are already displaced from other parts of Syria and have refused to reconcile with the Syrian government. The area also includes opposition fighters and some of Syria's most radical groups.

"Come on, leave Bashar!" hundreds of protesters chanted in Saraqeb, a town in eastern Idlib. "We will defend our revolution."

2:20 p.m.

A spokesman for a Syrian rebel alliance says the least the summit in the Iranian capital can do is avert a humanitarian crisis in the last bastion for the opposition in northwestern Syria.

Naji al-Mustafa, spokesman for the Turkey-backed National Front for Liberation, said Friday his fighters are prepared for battle. But they expect a major humanitarian crisis, a large wave of displacement and a lot of destruction and death if a Russia-backed offensive takes place.

Idlib and surrounding areas are home to more than 3 million people, nearly half of them already displaced from other parts of Syria.

Al-Mustafa said his rebel alliance is looking to Turkey's efforts to prevent the attack and "to protect Idlib." Turkey has deployed 12 observations points and hundreds of fighters that ring Idlib, separating them from government and allied fighters, as part of a de-escalation agreement with Russia and Iran.

1:55 p.m.

Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan have both arrived in Tehran for a trilateral summit on Syria.

The two presidents landed at Mehrabad International Airport.

They will attend the summit with Iranian President Hassan Rouhani.

The summit may determine whether diplomacy halts any military action ahead of an anticipated offensive targeting Syria's northwestern Idlib province.

1:25 p.m.

Activists and residents say warplanes have struck areas on the southern edge of the Syrian Idlib province, the rebels' last bastion, killing one and causing loud explosions and large plumes of smoke.

The airstrikes Friday come hours before presidents of Iran, Russia and Turkey meet in Tehran to discuss the war in Syria, with all eyes on a possible military offensive to retake bastion of Idlib.

Rami Abdurrahman, the head of the Britain-based Syrian Observatory for Human Rights, said a series of airstrikes struck a few villages in southwest Idlib and along the borders with the adjacent Hama province, targeting insurgent posts and killing a fighter. Abdurrahman said suspected Russian warplanes carried out the airstrikes.

Idlib province and surrounding areas are home to more than 3 million people.

12:55 p.m.

The spokesman for Iran's Foreign Ministry is calling a summit on Syria between Iran, Turkey and Russia an "invaluable opportunity."

Bahram Ghasemi wrote an opinion piece published across Iranian media on Friday that the summit in Tehran helps as all the nations "have faced similar challenges and joint threats by bullying foreign powers."

Ghasemi wrote: "The summit has double significance since all the three nations have faced ambitions and greediness of an illogical international big power." That refers to the United States, which has some 2,000 troops in Syria after its war against the Islamic State group.

The summit Friday between Iranian President Hassan Rouhani, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan may determine whether diplomacy halts any military action ahead of an anticipated offensive targeting Syria's northwestern Idlib province.

9:55 a.m.

The presidents of Iran, Russia and Turkey will meet in Tehran to discuss the war in Syria, with all eyes on a possible military offensive to retake the last rebel-held bastion of Idlib.

The summit Friday, the third between Iranian President Hassan Rouhani, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan, may determine whether diplomacy halts any military action.

Northwestern Idlib province and surrounding areas are home to about 3 million people — nearly half of them civilians displaced from other parts of Syria. That also includes an estimated 10,000 hard-core fighters, including al-Qaida-linked militants.

Iran, Russia and Turkey all have their own competing interests over Syria. All also face U.S. sanctions under the administration of President Donald Trump.