As many as 1,000 Turks have joined Islamic State, making Turkey one of the largest sources of fighters for the group trying to form a caliphate in Syria and Iraq, a media report says.

The New York Times, citing Turkish media and government officials, reported that among the people joining IS are disaffected youths attracted by the group's ideological appeal and by the money they can earn. One Turk who fought for IS was quoted by the paper as saying that the group pays fighters $150 a day.

Hundreds of foreigners, including people from the U.S. and Europe, have joined IS, the Times reported.

The U.S. has been pressuring Turkey's president, Recep Tayyip Erdogan, to better police the country's border with Syria, stop the foreign fighters from joining the battle, and stop IS from selling the oil it's producing from fields it captured, the Times reported.

Erdogan has resisted the pressure, citing 49 Turkish citizens that IS is holding hostage, the paper said.

The Turkish fighters the paper interviewed said they identified more with IS's extreme version of Islam than with the more moderate approach taken by Turkey's government.

On Monday, Turkish media reported Erdogan as saying that the Turkish military is drawing up plans for a possible "buffer zone" on Turkey's southern border, where it faces a threat from Islamic State militants in Iraq and Syria.

The government would weigh up the plans and decide whether such a move was necessary, Turkish television stations quoted Erdogan as telling reporters on his plane as he returned from an official visit to Qatarm, Reuters reported.

A presidency official confirmed he had made such remarks but did not specify where along the border the zone might be established and gave no further details.

