AZAZ, Syria — Turkish ground forces pushed into northern Syria's Afrin province on Sunday, media cited the prime minister as saying, as Ankara stepped up artillery attacks on a US-backed Kurdish militia it aims to sweep from its border.

NATO's second-largest army entered northern Syria shortly after 11:00 a.m. (0800 GMT), broadcaster HaberTurk cited Prime Minister Binali Yildirim as saying.

The Syrian-Kurdish YPG militia, supported by the United States but seen as a terrorist organization by Turkey, said it had repulsed the Turks and their rebel allies after fierce clashes.

Turkey aims to create 30 kilometer (19 miles) "safe zone" as part of its operation in northern Syria's Afrin province, broadcaster HaberTurk said on Sunday, citing Prime Minister Binali Yildirim.

So far, there were no wounded soldiers on in the opreration, HaberTurk cited Yildirim as saying

The fighting marks the second day of Turkey's new front in the nearly seven-year-old Syrian civil war.

Under what the Turkish government has called "Operation Olive Branch", Turkish air strikes on Saturday pounded positions of the Syrian-Kurdish YPG militia in the northern Afrin province.

The military said it had hit 153 targets so far, including shelters and hideouts used by Kurdish militants. The YPG has said Turkey's strikes killed six civilians and three of its fighters, and wounded 13 civilians.

The YPG has also accused Turkey of striking civilian districts and a camp for the displaced in Afrin.

"In its second day, #OliveBranchOperation continues to ensure peace and security for our people, protect Syria’s territorial integrity and eliminate all terrorist elements in the region," Turkish President Tayyip Erdogan's spokesman Ibrahim Kalin said on Twitter.

"Turkey expects its allies to support its fight against terrorism in all of its forms."

On land, the Turkey-backed Free Syrian Army rebels were also helping the operation in Afrin, Turkish officials said.

Intense bombardment continued on the region's Balia and Topal villages, the YPG said.

"Our people are holding on to their land and do not accept surrender ... we repeat our determination to protect our people in Afrin against the attacks," the YPG said overnight.

Turkey's state-run Anadolu news agency reported that four rockets fired from Syria hit the border town of Kilis overnight, damaging houses. Turkish security forces retaliated, it said.

The operation pits Turkey against Kurdish fighters allied to the United States at a time when ties between Ankara and Washington — NATO allies and members of the coalition against Daesh — appear close to a breaking point.

Turkey sees the YPG as an extension of the outlawed Kurdistan Workers Party (PKK), which has carried out a deadly, three-decade insurgency in Turkey's mainly Kurdish southeast.

The United States is backing the YPG in Syria, seeing it as an effective partner in the fight against Daesh. — Reuters