Albania and Greece have restarted negotiations to delineate maritime borders in the Ionian Sea.

Albania's Foreign Ministry said in a statement Monday the first round of talks was held in Tirana in a "constructive and cooperative climate."

The talks are needed because Albania's Constitutional Court nullified a 2009 agreement on the country's respective territorial claims to the sea's continental shelf and waters, which was signed by the conservative Democratic Party government ruling at the time.

The Socialists, then in opposition but governing Albania now, challenged the agreement in court, claiming it cost the country 225 sq. kilometers (86 sq. miles) of territorial waters.

Relations between Greece and post-communist Albania have remained uneasy, and the striking down of the Ionian Sea agreement was another area of tension.