Balkan neighbours Bulgaria and Macedonia have agreed to conduct joint air and land operations for border control and protection in the context of the migration crisis in the coming days, the government in Sofia announced on Thursday.

The agreement was reached in a telephone conversation between Bulgarian Prime Minister Boyko Borisov and Macedonian President Gjorge Ivanov.

The two leaders discussed options for disrupting the channels for smuggling migrants across the common border, the government press office said in a statement.

Macedonia has sealed its border with Greece earlier this month after Austria and other EU member states curbed to a trickle the daily intake  of asylum seekers. More than12,000 migrants have remained stuck at Idomeni, on the Greek side of the border, as a result. The few migrants who had forced their way into Macedonia earlier this week were sent back to Greece.

The Western Balkan route running from Greece via Macedonia and Serbia was closed to migrants and refugees last week after Slovenia and Croatia announced that only people who have valid visas and passports will be allowed to enter their territory. Serbia immediately followed suit by introducing reciprocal measures on its borders with Bulgaria and Macedonia.

In the conversation with Ivanov Borisov expressed concern about the plight of refugees and said that Bulgaria was going to send humanitarian aid to refugees in Macedonia after shipping such assistance to the people stuck at Idomeni, according to the statement.

Borisov also reiterated Bulgaria’s position that efficient control of all of the EU’s external borders and not just the borders of the bloc’s free-travel Schengen zone is key to curbing the flow of irregular migrants into Europe.

EU member Bulgaria, bordering both Turkey and Greece, is not member of the Schengen area. Concerns about possible shifting of migration routes to Bulgaria have increased since the closing of the Western Balkans route.