BEIRUT — Turkey’s president said Sunday that his troops and allied Syrian fighters have reached the heart of the Islamic State stronghold of al-Bab in northern Syria and will eventually join the effort to recapture Raqqa, the extremists’ de-facto capital in Syria.
Recep Tayyip Erdogan said ISIS fighters have begun deserting al-Bab, which has been under attack for weeks.
The Britain-based Syrian Observatory for Human Rights, which relies on a network of activists inside Syria, said it could not confirm that Turkish troops had entered al-Bab’s center, as fighting continued on the edges of the town.
The Turkish-backed opposition forces advancing from the north have been racing to seize al-Bab before Syrian government forces reach the town from the south. The Turkish-backed forces are still a long way from Raqqa, which is mostly surrounded by US-backed Syrian Kurdish forces.
Last week, the Kurdish-led Syria Democratic Forces launched a new phase in its Raqqa offensive, aiming to capture towns and villages east of Raqqa. The US-led coalition has targeted several bridges across the Euphrates River in support of the operation.
Turkey is leading Syrian opposition forces in a broad operation called ‘‘Euphrates Shield’’ against both ISIS and the SDF. Ankara views the Kurdish group that dominates the SDF as a terrorist organization because of its links to Kurdish insurgents in Turkey.
‘‘After al-Bab is about to be over, the period following that will be Manbij and Raqqa,’’ Erdogan said, referring to the northern town of Manbij, which was captured by the SDF last year after weeks of deadly fighting with ISIS.
‘‘Right now al-Bab, whether by us or by the Free Syrian Army, is now besieged on all four sides and our forces along with the Free Syrian Army have entered the center,’’ he said.
The Observatory reported intense clashes and Turkish airstrikes and shelling on the northern, western, and southern edges of the town, which is 25 miles south of the Turkish border.
In Lebanon, the leader of the militant Hezbollah group, which is fighting alongside President Bashar Assad’s forces, said it supports a Dec. 30 cease-fire between the government and the opposition that was brokered by Turkey and Russia.
‘‘We are with every measure that stops the shedding of blood and paves the way for a political solution’’ in Syria, Hassan Nasrallah said in a speech aired in Beirut. He was responding to claims by opposition media that Hezbollah opposes the truce.
The Syrian government, the opposition, and their various state backers are gearing up for the resumption of UN-brokered talks in Geneva, after the last round stalled in April last year.
Rebels and Western- and Saudi-backed opposition groups in exile are preparing to name 20 delegates to the talks, according to Yahya al-Aridi of the High Negotiations Committee.
Diplomatic contacts picked up between the various sides in December, with rebels and the government pledging to honor a national cease-fire brokered in Ankara.
The truce has not held. The two sides met again for talks in Astana, Kazakhstan last month, ahead of the planned resumption of the Geneva talks in about one week’s time.
Kazakhstan’s Foreign Ministry said Saturday it was inviting government and opposition officials and delegates from Russia, Turkey, and Iran for preparatory talks in Astana on Thursday.
On Saturday, Iran’s Supreme National Security Council authorized Russia to fly its fighters over Iranian airspace to support operations in Syria, the state’s semiofficial Tasnim news agency reported.
In August, Iran confirmed that Russian bombers launched airstrikes from near the Iranian city of Hamedan to hit targets in eastern Syria. Iran is a staunch supporter of the Syrian government.
In al-Bab, Turkish aircraft and artillery pounded ISIS positions as allied opposition forces grabbed new blocks in the town, according to the Syrian Observatory. The Turkish-backed Ahrar al-Sham militia announced Saturday that opposition forces had taken the city’s silos and sports complex in its southwestern districts.
The coalition’s operations room released a video on social media showing its fighters at the gates of the Hikma hospital.
About 100,000 residents lived in al-Bab before the start of the Syrian civil war, six years ago. The town is about 19 miles from the Turkish border.
Turkey is the opposition’s chief backer in Syria’s multisided civil war. It has deployed troops, tanks, artillery, and its air force inside the country as part of the northern Syria operation.
Turkey’s Anadolu news agency began reporting Turkish troop fatalities in al-Bab on Dec. 21. That week, 16 Turkish soldiers were killed in clashes or ambushes by the Islamic State in the town.
The military Saturday announced the death of another soldier in the fighting in al-Bab. The death brings the total number of Turkish troops killed in the military operation in northern Syria to 65.