Turkish President Tayyip Erdogan addresses a news conference at the Presidential Palace in Ankara, Turkey, April 18, 2018. Murat Cetinmuhurdar/Presidential Palace/Handout via REUTERS

ISTANBUL (Reuters) - Turkey and its Syrian rebel allies have lost "hundreds" of fighters in total since the start of a campaign in northwest Syria three months ago, President Tayyip Erdogan said on Saturday, with the rebels suffering the bulk of the losses.

Turkey and its Free Syrian Army (FSA) allies launched the operation, dubbed "Olive Branch" by Ankara, in January and have since swept the Syrian Kurdish YPG from the Afrin region.

Erdogan has previously threatened to push further east, a move that would ratchet up tension in Syria's multi-sided conflict.

"Alongside our 56 martyrs, the FSA army had hundreds of martyrs," Erdogan told Turkey's NTV in an interview broadcast live.

Turkey sees the YPG as an extension of the outlawed Kurdistan Workers Party (PKK), considered a terrorist group by the United States and Europe. The PKK has waged a three-decade insurgency in Turkey's largely Kurdish southeast that has left some 40,000 people dead.

The United States has trained and backed the YPG militia in the fight against Islamic State in Syria. That support has infuriated Erdogan and strained ties between Washington and Ankara, both NATO allies and members of the coalition against Islamic State.

(Reporting by Ali Kucukgocmen; Writing by David Dolan; Editing by Andrew Bolton)