Turkish President Recep Tayyip Erdogan called for a 30-kilometer (19-mile) security corridor on Turkey’s border with Syria in a phone call with Russian President Vladimir Putin, Erdogan’s office said Sunday.

Referring to Kurdish militants that Ankara considers terrorists, Erdogan reiterated the “importance and urgency” of creating the corridor in northern Syria in accordance with a 2019 agreement between Turkey and Russia, the statement added.

The call came three weeks after Turkey launched air and artillery strikes in Syria and Iraq in response to a bomb attack in Istanbul on Nov. 13 that killed six people and wounded dozens. The Turkish government has blamed the bombing on the Kurdistan Workers’ Party, or PKK, and its Syrian affiliate the People’s Protection Units, or YPG.

Both groups have denied involvement in the attack.

The PKK has waged a 38-year insurgency against Turkey that has led to the loss of tens of thousands of lives. It is listed as a terrorist organization by Turkey, the United States and the European Union. The YPG, however, is not designated as a terror group by Washington or Brussels and has spearheaded the U.S.-led fight against the Islamic State group in Syria.

Erdogan has threatened to follow up strikes on northern Syria with a ground offensive. A planned Turkish invasion earlier this year was halted amid opposition by the U.S. and Russia, both of which have military posts in the region.

Under a 2019 deal signed with Turkey, Russia promised to establish a buffer zone between the Turkish border and YPG forces that would be controlled by the Syrian army and Russian military police. The agreement was not fully implemented although both Russian and Syrian government forces are present in the border region, as well as some U.S. troops.

Moscow, which is the main backer of Syrian President Bashar Assad, has closely cooperated with Turkey in northern Syria in the past and in recent months has pushed for reconciliation between Ankara and Damascus.

The call between Erdogan and Putin follows a visit to Turkey this week by Russian Deputy Foreign Minister Sergei Vershinin for talks on the situation in Syria.

Erdogan’s office said the presidents also discussed energy — Russia has offered to make Turkey a hub for the sale of its natural gas — as well as the deal brokered by the United Nations and Turkey that safeguards the export of Ukrainian grain from its Black Sea ports.

Erdogan told Putin that the agreement could be expanded to “different food products and other commodities gradually,” his office added without providing further detail.