The Islamic State group is seeing some defections in its leadership in Syria as two senior commanders have fled in recent days to territory held by rebels fighting the Syrian regime, local sources and a monitoring group said.

Two high-ranking commanders of Tunisian origin and some close followers with Egyptian backgrounds left the Syrian city of Raqqa, Islamic State's de facto capital, and headed to the rebel-held city of Idlib, in northwestern Syria, according to reports on the ground.

The militant group's "internal situation is getting worse day by day," said Hussam Eesa, spokesman for Raqqa Is Being Slaughtered Silently, an activist group that reports on IS movements in the city.

The activist group, which has monitors inside Raqqa, verified the defections of IS commanders, Eesa said.

FILE - Militants of the Islamic State group hold u FILE - Militants of the Islamic State group hold up their weapons and wave flags on their vehicles in a convoy on a road leading to Iraq, while riding in Raqqa, Syria. The undated file photo was released by a militant website. FILE - Militants of the Islamic State group hold up their weapons and wave flags on their vehicles in a convoy on a road leading to Iraq, while riding in Raqqa, Syria. The undated file photo was released by a militant website.

IS has been attempting to fortify its hold on Raqqa as a Kurdish-dominated militia alliance has mounted a slow assault on villages north of the city once controlled by IS. U.S. jets have bombed the outskirts of the city.

U.S. officials vowed in October that an offensive will clear out IS militants from Raqqa.

Noteworthy defections

The two IS leaders who fled Raqqa "are noteworthy because they are reportedly Tunisian sheikhs who were senior members of IS who helped formulate strategic external attacks in the West," said Nicholas A. Heras, a Middle East researcher at the Washington-based Center for a New American Security.

IS is fighting multiple battles with U.S.-backed Iraqi and Kurdish forces in Syria and Iraq — especially in strongholds in Mosul and around Raqqa. Amid mounting IS casualties in Iraq, there are reports of IS leaders fleeing to Raqqa where dissension among the leadership is reportedly growing over how to fight the battles, analysts say.

"IS has a central leadership in Iraq and Syria," said Sadradeen Kinno, a Syrian reporter who closely follows Islamist groups in the country. "Whenever an internal strife arises, some members want to survive" by leaving, he said.

This image posted on the Twitter page of Syria's a FILE - This image posted on the Twitter page of Syria's al-Qaida-linked Nusra Front, April 25, 2015, shows Nusra Front fighters in the town of Jisr al-Shughour, Idlib province, Syria. FILE - This image posted on the Twitter page of Syria's al-Qaida-linked Nusra Front, April 25, 2015, shows Nusra Front fighters in the town of Jisr al-Shughour, Idlib province, Syria.

The two leaders who fled, Abu Zur al-Tunisi and Bilal al-Shawwash, have reportedly joined the Jabhat Fateh al-Sham — formerly known as the al-Nusra Front, which has been fighting against the Syrian government since the country's civil war broke out in 2011.

Idlib province

Fateh al-Sham, which severed ties with al-Qaida in July, controls much of Idlib province and is considered the main Islamist rival to IS in Syria.

The defections "demonstrate that Fateh al-Sham is the organization best positioned to accept any influx of foreign jihadist commanders and their fighters that defect from [IS]," analyst Heras said.

"Global Salafist jihadist operatives, like [the] two Tunisian sheikhs, still view Fateh al-Sham as an al-Qaida organization that is successfully building a safe haven in Syria for them to continue to plan to wage jihad against the West," he said.

The presence of former IS commanders in the rebel group "would encourage many other foreign members [of IS] to defect," Syrian activist Eesa said.

IS has lost several top commanders in U.S. coalition airstrikes. IS this week named Abu Hassan al-Muhajir as its new spokesman, replacing Abu Muhammad al-Adnani who was also killed in a U.S. drone strike near the Syrian town of al-Bab in late August.