BEIRUT (AP) — Airstrikes killed at least 23 civilians on Tuesday in one of the last pockets of Islamic State-controlled territory in Syria, according to Syrian state media and an opposition-linked monitoring group, as U.S.-backed forces in the area announced they have resumed their campaign against the extremists.

The Britain-based Syrian Observatory for Human Rights said it was not clear if the airstrikes in the Hassakeh province were carried out by the U.S.-led coalition or the Iraqi air force. It said the strikes killed 10 children, six women and seven elderly people. The state-run Syrian News Agency said 25 civilians were killed in the airstrikes south of the town of Shadadi, blaming the U.S-led coalition.

The strikes took place in an area where the U.S.-backed and Kurdish-led Syrian Democratic Forces are battling IS.

In an email to The Associated Press, the U.S-led coalition said initial reports suggest there were no coalition airstrikes in the area where the deadly airstrikes are said to have taken place.

Lelwa Abdullah, an SDF spokeswoman in the adjacent Deir el-Zour province, said Tuesday the final phase of a large operation against IS in eastern Syria has begun. She said the SDF will "liberate those areas and secure the Syrian-Iraqi border and end the IS presence in eastern Syria once and for all."

The SDF had redeployed hundreds of its forces to western Syria after Turkish troops attacked the Kurdish-held Afrin enclave earlier this year, effectively putting operations against IS on hold.

Abdullah said IS attacks have increased in recent weeks in parts of eastern Syria near the border with Iraq as the extremist group seeks to regroup. She said the clearing operations will take place with the help of the U.S.-led coalition and Iraqi forces across the border.

The U.S. State Department said the days of IS controlling territory in Syria "are coming to an end," and that the renewed operations are intended to "liberate the final ISIS strongholds in Syria."

President Donald Trump has said he wants to pull out U.S. troops as soon as the extremists are defeated. But State Department spokeswoman Heather Nauert said the U.S. will "ensure that there is a strong and lasting footprint in Syria such that ISIS cannot return."

Elsewhere in Syria on Tuesday, more than three dozen Syrians held for years by al-Qaida-linked insurgents in the country's northwest were released as part of a deal to hand over areas around Damascus to the government, state media reported.

State-run Al-Ikhbariya TV broadcast images of the released men, women, children, who arrived by bus at a government-controlled checkpoint in Aleppo province. Many were in tears, and they could be seen kissing and hugging Syrian soldiers. The captives had been held by the insurgents in northern Syria since 2015.

Insurgents have agreed to a series of evacuation deals for areas around the capital that have been besieged for years and subjected to heavy bombardment by government forces. The U.N. and rights groups have criticized the deals, saying they amount to forced displacement.

The agreement concerns Yarmouk, a Palestinian refugee camp that was a built-up residential area before the civil war. IS militants still control parts of the camp and a neighboring area, where they are battling government forces.

The 42 people freed on Tuesday are the first batch of more than 80 to be released. Under the deal, fighters from the al-Qaida-linked Hayat Tahrir al-Sham group will withdraw from Yarmouk, while about 5,000 people in Foua and Kfraya, two northwestern villages besieged by insurgents, will be allowed to relocate to government-held areas.

Al-Ikhbariya said nearly 20 wounded or ill from the two besieged villages were evacuated Tuesday. But the evacuation has apparently stalled amid security concerns, with the residents asking that they all be evacuated together instead of in batches.

The Observatory said five buses carrying around 200 insurgents from Yarmouk arrived at the handover area south of Aleppo.

The U.N. has warned of "catastrophic consequences" for the remaining inhabitants of Yarmouk as the fighting continues.

The camp was established in 1957 for Palestinians who fled the 1948 war with Israel, and later evolved into a densely populated urban neighborhood that was home to tens of thousands of Palestinians and Syrians. It has seen heavy fighting since the early days of the seven-year-old civil war, and IS pushed into the district in 2015.

"Yarmouk and its inhabitants have endured indescribable pain and suffering over years of conflict," Pierre Krähenbühl, the head of the U.N. agency for Palestinian refugees, said last week.

The latest fighting has displaced around 5,000 civilians from Yarmouk into the neighboring area of Yalda, the U.N. said. It's not clear how many civilians remain in Yarmouk.

Later on Tuesday, state-run Al-Ikhbariya TV said rebels have agreed to allow government forces to return to the countryside north of Homs, the country's third largest city, and re-establish state institutions.

Rebels will have the option of pledging their allegiance to the government or relocating to rebel-held territory in northern Syria. The station says the international highway running through the region will reopen in three days.