Abraham resigned on Monday, less than a week after being appointed, citing Croatia's decision to withdraw from the arbitration agreement signed by the two countries in 2009 as the reason for the move.

Abraham informed the tribunal that he had agreed to his appointment in the hope that this "would help restore confidence between the parties and the arbitral tribunal and to allow the process to continue normally, with the consent of both parties".

Having realized "the current situation cannot meet that expectation", the judge considered it was "no longer appropriate" for him to serve as arbitrator in the present proceedings, a press release from the Hague reads.

The Permanent Court of Arbitration, which acts as the secretariat for the tribunal, said today it was now up to Slovenia to appoint an arbitrator to replace Abraham with 15 days.

While regretting Abraham's decision, the government responded that Slovenia planned to decide on the appointment of a new arbiter. It has 15 days to do so in line with the arbitration treaty.

"Slovenia will take the decision on the appointment of a new arbiter in due time," the government said in a press release, hopeful that the full line-up of the tribunal would "soon continue and complete its work in line with the arbitration agreement".

The government said it did "not understand the reasons" for the resignation. "We believe the court must continue its work, it should not allow Croatia's arbitrary and unilateral withdrawal to halt the entire procedure."

The Foreign Ministry also expressed regret in a press release, adding that it had rejected via diplomatic channels Croatia's wish to withdraw from the arbitration.

The European Commission meanwhile said it was keeping a close eye on the procedure, adding that it "supports and encourages dialogue between the two parties in order to find a common solution."

Abraham's decision has caused dismay on the political scene, with the centre-right opposition in particular faulting the government.

Democrats (SDS) leader Janez Janša tweeted to PM Miro Cerar it was "Time to go. High time", and also pointed to media speculations that not getting the entire the Bay of Piran was Slovenia's price to pay for hosting recently Russian PM Dmitry Medvedev.

MP Jožef Horvat of the opposition New Slovenia (NSi), who chairs the parliamentary Foreign Policy Committee, said he would convene an emergency session of the committee as soon as possible, adding that a summit of parliamentary party heads should also be held.

Opinions on the successor of Abraham vary greatly among experts. While maritime law professor Marko Pavliha believes a Slovenian should be appointed, former FM Ivo Vajgl advises a foreign expert and analyst Boštjan Udovič says the appointment should be left to the tribunal.

Abraham, the president of the International Court of Justice, was appointed by the Slovenian government on 28 July.

He replaced Jernej Sekolec, who resigned as arbitrator after a Croatian paper released recordings of his phone conversations with a Slovenian Foreign Ministry official in apparent breach of the requirement that he should have acted independently of the parties to the dispute.