BRUSSELS, Sept. 10 (Xinhua) -- Four NATO warships were leaving the Black Sea after exercises with Romanian and Bulgarian ships, the alliance said Wednesday.

    The NATO ships arrived in the Black Sea on Aug. 21. Wednesday is the deadline for their departure under the Montreux Convention, which limits Black Sea naval deployments to 21 days for non-Black Sea navies.

    Russia criticized the deployment of NATO ships in the Black Sea as it took place at a sensitive time following the Georgia-Russia conflict.

    In response, NATO said the deployment had been planned more than a year ago and was not linked to the Georgia crisis.

    NATO said the ships will operate in the Mediterranean following their departure from the Black Sea.

    The warships, known as Standing NATO Maritime Group One, are a group of frigates and destroyers from member nations. They conduct exercises together round the year to promote inter-operability.

    The group of ships comprises the Spanish SPS Adm Juan de Bourbon, the German FGS Luebeck, the Polish ORP General K Pulaski, and the U.S. frigate USS Taylor. A fifth ship, the Canadian frigate HMCS Ville de Quebec, was recently detached from the group to escort World Food Program (WFP) shipments off the coast of Somalia.