Kurdish fighters in the northwestern Syrian region of Afrin have vowed to continue fighting Turkey's forces and Turkey-backed rebel groups, by shifting from direct confrontation to guerrilla tactics.

Meanwhile, the Free Syrian Army (FSA) rebels and Turkish forces, who gained complete control of the city of Afrin on Sunday, continued their activities to secure the city, with troops searching for landmines and other explosive devices in the area.

"Our forces are present all over Afrin's geography. These forces will strike the positions of the Turkish enemy and its mercenaries at every opportunity," Othman Sheikh Issa, a representative of the Kurdish People's Protection Units (YPG), said in a televised statement on Sunday evening.

"Our forces all over Afrin will become a constant nightmare for them," he added.

"Many of the terrorists had turned tail and run away already," President Recep Tayyip Erdogan said in a speech in western Turkey on Sunday after he announced that Afrin's city centre was captured at 8:30am local time (05:00 GMT) on the same day.

He said 3,603 "terrorists had been neutralised" in Afrin since the launch of the cross-border operation on January 20.

Erdogan said the Turkish flag and the flag of the Syrian opposition fighters were raised in the city, previously controlled by the YPG.

Later on Sunday, limited fighting was reported in some pockets in Afrin.

"Our special forces and members of the Free Syrian Army are cleaning the remains and the traps they left behind," Erdogan said. "In the centre of Afrin, symbols of trust and stability are waving instead of rags of terrorists."

Turkey - together with the FSA - launched in January the military operation into Afrin in the northwest of Syria to vanquish the US-backed YPG fighters near its border.

'More to do'

The Syrian Observatory for Human Rights, a UK-based war monitor, previously said at least 150,000 civilians fled the city since last Wednesday.

Turkey's government spokesman Bekir Bozdag said the military campaign would continue to secure areas around Afrin and make sure food and medicine were available.

"We have more to do. But the project of building a terrorism corridor and building a terrorist state is over," he said.

Afrin şehir merkezinden ilk görüntüler. pic.twitter.com/DQdGzWSAmr — TSK (@TSKGnkur) March 18, 2018

Turkey considers the Kurdish Democratic Union Party (PYD) in Syria and its armed wing YPG to be "terrorist groups" with ties to the banned Kurdistan Workers' Party (PKK).

The PKK has waged a decades-long armed fight against the Turkish state that has killed tens of thousands of people.

The YPG had come to control large swaths of northern Syria, including Afrin, in the course of the eight-year Syrian war, particularly through fighting against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group in an US-backed umbrella organisation named Syrian Democratic Forces (SDF).

The US support for the Kurdish-dominated SDF has infuriated Turkey and created the ongoing diplomatic crisis between the two NATO allies.