By Hamdi Alkhshali, Schams Elwazer and Joe Sterling, CNN

(CNN) -- ISIS is said to have suffered key setbacks in Syria, with US-led coalition forces grabbing more turf in the terror group's self-declared capital of Raqqa and the Syrian military seizing a key eastern city.

The conflict, which started in 2011, has resulted in the deaths of an estimated 400,000 Syrians and the displacement of millions.

ISIS' hold on Raqqa has eroded. Eighty-five percent of the city has been liberated from the terror group, the US-led Combined Joint Task Force said Saturday.

In a written statement, the task force told CNN that "steady progress" was being made in defeating ISIS in the group's stronghold.

The US-backed Syrian Democratic Forces said it believes few hundred militants remain in the city.

Fighting is expected in the days ahead, but a specific timeline for the defeat of ISIS hasn't been determined, it said.

About 100 ISIS soldiers had surrendered; they were removed from Raqqa, and 1,500 civilians were able to evacuate the city safely this week, the task force said.

Evacuation plan

As fighting persists, civilians in Raqqa were to leave in an evacuation plan brokered between tribal elders and a local council, the US-led coalition said.

People departing the city will be subject to search by the SDF, a coalition of mostly Kurdish and some Arab militias.

The arrangement excludes foreign ISIS fighters but does permit the group's local fighters to withdraw along with civilians, the coalition said.

Coalition spokesman Col. Ryan Dillon said it's important that people who leave Raqqa are "monitored and tracked" and that local ISIS affiliates don't get back into the conflict.

"This arrangement was reached by our partners and their local affiliates," Dillon said. "We might not fully agree with our partners at all times, but we have to respect their solutions to their own issues."

Dillon vowed that ISIS will be defeated in Raqqa "relatively soon" and then elsewhere in the "few remaining areas where ISIS still holds territory."

The Syrian army recaptured the city of al-Mayadeen on Saturday after heavy fighting against ISIS, the state-run Syrian Arab News Agency said. Al-Mayadeen is nearly 45 kilometers (28 miles) from Deir Ezzor.

The army killed large numbers of ISIS fighters and destroyed their weapons and equipment, SANA reported.

"Army units are chasing remnants of ISIS terrorists out of al-Mayadeen while the engineering units are clearing land mines left in the town," the agency said.

SANA said control of the city is a key step toward ousting the group in the Euphrates region.

US officials believe ISIS has housed much of its leadership as well as up to 10,000 fighters in the Middle Euphrates River Valley.

Syria condemns Turkey's 'incursion'

On another front, Syria condemned what it called an "incursion" of Turkish troops into the northwestern province of Idlib and demanded immediate "unconditional withdrawal," state media reported Saturday.

SANA quoted a Foreign Ministry source as saying the move "constitutes blatant aggression on the sovereignty and territorial integrity of Syria and a flagrant violation of international law and norms."

Turkey -- which shares a border with Syria -- said Friday it began "establishing observation posts in Idlib to monitor de-escalation zones that aim to bring an end to the conflict," Turkey's state-run Andolu Agency said.

The outlet said the operation was launched under a May deal between Turkey, which backs groups opposed to Syrian President Bashar al-Assad, and Russia and Iran, who support Assad's regime.

The deal aimed "to establish a number of de-escalation zones so as to ensure the continuation of a cease-fire" the three countries agreed on in December.

Such zones would "enhance the effectiveness of the cease-fire, end conflicts, bring humanitarian aid to those in need (and) establish the necessary conditions for the return of those displaced," the Turkish military said.

The-CNN-Wire

™ & © 2017 Cable News Network, Inc., a Time Warner Company. All rights reserved.