ISTANBUL - Turkey is facing calls for restraint by its Western allies as well as Russia and Iran after Ankara's forces launched a military offensive against a Syrian Kurdish militia Wednesday.

"[Turkish President Recep Tayyip] Erdogan cannot step back. He was under so much public pressure," said Huseyin Bagci, an international relations professor with Ankara's Middle East Technical University. "He could not postpone this [operation]. He has put his credibility on the line with this operation."

Operation Peace Spring was launched just three days after U.S. President Donald Trump, in a telephone conversation with Erdogan, decided to pull U.S. forces from northern Syria, paving the way for the Turkish offensive.

For months, Turkish forces have been massed on the Syrian border facing off against the Kurdish-led Syrian Democratic Forces, the SDF. Ankara designates the main force within the SDF, known as the YPG, as terrorists. The YPG is a critical ally in the Washington-led war against the Islamic State terror group.

The SDF has reportedly announced an end to anti-Islamic State operations. The announcement will likely embolden critics of the Turkish operation in Washington who warned that the war against Islamic State is under threat. Tens of thousands of jihadists and their families are held in detention camps by the SDF.

"Turkey gave assurances to Trump to get ISIS people and control them," said Bagci. "Turkey has experience of fighting ISIS [Islamic State] and dealing with their detainment; we have many ISIS members in Turkey's prisons."

Observers warn many of the Islamic State detention camps are outside Turkey's planned 32-kilometer buffer zone into Syrian territory.

Russia, Iran

Turkey is also set to face growing pressure from Russia and Iran. While backing rival sides in the Syrian civil war, the three countries are cooperating in efforts to end the conflict. Russia and Iran back the Syrian government; Turkey has been fighting with the Free Syrian Army, or FSA.

Erdogan spoke to Russian President Vladimir Putin hours before the start of the military operation. The Turkish president told Putin the process would "contribute to Syria's peace and stability and ease the path to a political solution," a spokesman for the Turkish presidency said.

Earlier Wednesday, Russian Foreign Minister Sergey Lavrov called on Ankara to find a diplomatic solution. "All issues should be settled through dialogue between the central government in Damascus and the representatives of the Kurdish communities which primarily inhabit these territories," he said.

Lavrov's stance echoes that of his Iranian counterpart, Javad Zarif. "The only way to maintain the security of Turkey is the military presence of the central government in the border areas," Zarif said Sunday.

Analysts say Russia's and Iran's priority is restoring Damascus' control over Syrian territory. Ankara's military operation will see a significant expansion of Turkey's military footprint in Syria.

Syrian refugees

Erdogan's intention to send back up to 2 million Syrian refugees to the planned buffer zone in Syria is also likely to ring alarm bells in Tehran, Moscow and Damascus.

"Assad is very happy with the present situation," said international relations lecturer Soli Ozel of Istanbul's Kadir Has University, referring to Syrian President Bashar al-Assad. "I mean the demographic composition of the country changed. The Sunnis, Sunni Arabs are no longer an overwhelming majority," Ozel said.

"I just don't think that they will let Turkey change the demographics," he added. "I think the Russians will say no to that. The Iranians already said no to this."

However, with Turkey hosting around 3.6 million Syrian refugees and growing Turkish public discontent, analysts say Erdogan won't back down.

"The primary concern Turkey has is to get back as soon as possible as many refugees, so the tension in the country is reduced," said Bagci. "This is the priority of Turkish foreign policy at the moment. Ankara has already prepared plans for the refugees to return."

Kurdish militia

Analysts suggest Moscow and Tehran are likely to see the Turkish military operation as an opportunity to achieve a long-term goal of prying the Kurdish militia from Washington.

"We are considering a partnership with Syrian President Bashar al-Assad, with the aim of fighting Turkish forces," Mazlum Kobane, the SDF commander, said Tuesday.

Until now, the Kurdish militia has resisted Russian and Iranian overtures to realign with Damascus. Kurds under Assad's rule were brutally oppressed. Faced by the might of the Turkish army, NATO's second largest, analysts suggest the Kurdish militia are now caught in a no-win situation.