ANKARA, Turkey — Fighting in northern Syria between Turkey-backed Syrian rebels and Islamic State militants killed at least 15 rebels as the opposition pressed toward a town of symbolic importance for the extremists, an activist group and Turkish officials said Monday.

The Syrian government continued to strike besieged, rebel-held parts of eastern Aleppo, hitting the area’s largest hospital, according to activists. A monitoring group said more than 400 civilians have been killed in and around Aleppo since the collapse of a U.S. and Russian-brokered cease-fire two weeks ago, mainly in the rebel-held east.

In central Syria, meanwhile, two suicide bombers struck the city of Hama close to an office of President Bashar Assad’s Baath party, killing three people and wounding at least 11, state news agency SANA said. IS claimed responsibility in an online statement.

SANA said a suicide bomber detonated his explosives-packed belt in Hama’s al-Assi Square, and another suicide bomber struck 15 minutes later. One of SANA’s photographers, Ibrahim Ajaj, was wounded as he was covering the explosions, the agency said, adding that he is in stable condition.

The Britain-based Syrian Observatory for Human Rights said the two explosions killed three people and wounded 14.

Suicide attacks in government-held areas are not uncommon, but blasts in the city of Hama, which is firmly under the control of Assad’s forces, have been rare. The twin bombings came as various insurgent groups have been on the offensive north of the city.

Another suicide bombing struck a Kurdish wedding outside the northeastern Syrian city of Hassakeh, killing at least 22 people, according to the Observatory, which said the toll was likely to rise. The Kurdish Hawar news agency confirmed the attack but did not provide a toll. The state new agency SANA said 20 were killed and 55 were wounded in the wedding. There was no immediate claim of responsibility.

The death toll among the Syrian rebels near the Turkish border is the highest since Turkey sent troops and tanks into Syria in August to help rebels recapture IS strongholds in the area and curb the advance of a Syrian Kurdish militia, which Ankara views as an extension of Turkey’s outlawed Kurdish separatists.

Turkish military officials said 15 Syrian opposition fighters were killed and about 35 wounded in their offensive, which seeks to capture seven residential districts south of the town of al-Rai. The officials spoke on condition of anonymity in line with regulations.

The Observatory, which relies on a network of activists across Syria, said 21 rebels were killed and more than two dozen wounded, adding that many of the casualties were due to land mines and booby-traps planted by the extremists.

The Observatory said the Turkey-backed rebels are trying to reach the town of Dabiq, which occupies a central place in IS propaganda.

The extremists, citing ancient prophecy, believe Dabiq will be the scene of an apocalyptic battle between Christianity and Islam. The group named its online magazine after the town, which it has occupied since August 2014.

The Observatory said IS has been preparing for the battle in Dabiq for weeks, planting mines and explosives and sending some of its most experienced fighters to defend the town.

The epicenter of the civil war remains in Aleppo, however, where Syrian and Russian warplanes have been pounding rebel-held areas since the breakdown of the cease-fire on Sept. 19.

The Observatory said Russian and Syrian warplanes, and government artillery, have killed at least 387 civilians in rebel-held Aleppo and its rural surroundings, including 72 children and 24 women, since the truce broke down. In the rebel-held part of the city alone, 294 were killed. The group recorded 19 civilians killed in government-held Aleppo.

In the offensive, which includes a limited ground operation, health facilities have repeatedly come under attack.

On Monday, Adham Sahloul of the U.S.-based Syrian American Medical Society, which supports various hospitals in rebel-held areas, said a bunker-busting bomb gouged out a 10-meter-deep crater where it landed near the entrance of one of the largest emergency hospitals in the rebel-held part of Aleppo. This is the third time the hospital has hit in a week, including once with several bombs. This time, the attack rendered it “not salvageable,” said Sahloul.

Sahloul said at least three maintenance staff were killed, including one found 100 meters (330 feet) away, apparently thrown by the impact of the explosion.

The workers were carrying out repair work at the hospital following last week’s attacks. Rescue workers are still searching for people under the rubble, and there were fears the building would collapse, Sahloul said. He added that since 2014 most of the hospital’s facilities were set up underground to protect it.

The Observatory confirmed the bombing, but put the death toll at six.

In the central Hama province, a medical relief group and the Observatory said airstrikes have damaged and put one of Syria’s most secure hospitals, which had been dug into a mountain, out of service.

The International Union of Medical Care and Relief Organizations, or UOSSM, said the Dr. Hasan Al-Araj Hospital — also known as “Cave Hospital” — was struck twice on Sunday.

The Observatory said Russian warplanes carried out the attacks that hit the hospital, adding that it’s one of the largest hospitals in rebel-held parts of the country. UOSSM said there were minor injuries from the attack.

Dr. Abdallah Darwish, the hospital’s director and health care chief in Hama province, was quoted in the UOSSM statement as saying that the hospital was likely struck by “bunker-buster” missiles as it was “well-fortified in a cave and impervious to previous attacks.”

The bomb completely destroyed the hospital’s emergency ward and caused major damage throughout the facility, he said.

“These vicious and atrocious campaigns are literally choking the life out of civilians, they are deplorable and unacceptable,” said Dr. Khaula Sawah, CEO of UOSSM USA.

Associated Press writers Bassem Mroue in Beirut, and Albert Aji in Damascus, Syria, contributed to this report.