Turkey has unilaterally suspended the migrant readmission agreement with Bulgaria, media sources say.

Ankara has already informed Bulgaria's ministries of interior and foreign affairs about the move which was personally ordered by President Recep Tayyip Erdogan, according to daily 24 Chasa.

The Turkish Embassy has meanwhile said Ankara has not halted its activities with regard to the agreement.

Bulgaria's Prime Minister Boyko Borisov has meanwhile commented on the reports and has made clear no document has arrived to Bulgarian institutions informing the agreement is suspended.

"But of 200 refugees we returned we have 200 refusals," Focus News Agency quotes him as saying.

News website Dnevnik.bg quotes Borisov as saying he will look for "diplomatic means" to talk with Ankara over the agreement.

He also vowed there would be consequences for Foreign Minister Daniel Mitov and Defense Minister Nikolay Nenchev if they had taken on any commitments with regard to a joint naval units without his approval.

Several national news outlets quote government sources as saying the decision is tied to Bulgaria's refusal to join a Black Sea naval unit against Russia put forward by Romania's President Klaus Iohannis during his meeting with Borisov on Wednesday.

Reportedly, the unit should involve Bulgaria, Romania, Ukraine, Turkey, and the United States.

Borisov, however, told Iohannis he did not want another war in the Black Sea.

According to 24 Chasa's report, it is not clear whether proposal extended by Iohannis is different to the one discussed by Defense Minister Nenchev and his Romanian counterpart Mihnea Motoc in Brussels on Wednesday. Nenchev announced after meeting Motoc that Bulgaria was ready to send 400 troops to a Romania-based multinational brigade if NATO approved the concept.