Macedonian Foreign Minister Antonio Milososki told the court that the suit was a straightforward case of Greece breaking the terms of a 1995 agreement by blocking Skopje's accession to NATO.

"In the case before you we do not seek resolution of the name difference either directly or indirectly. This is and remains the object of the mediation process under the auspices of the UN," Milososki said.

"What do we seek in bringing this case? This case has been brought to ensure that the respondent [Greece] upholds one of its key obligations under the 1995 Interim Accord. Nothing more and nothing less," Milososki told the court in an opening speech.  

Macedonia sued Greece at the ICJ in 2009 for blocking its accession to NATO in 2008 over Macedonia's unresolved name dispute.

Macedonia argues that the blockade violates the 1995 UN-brokered Interim Accord, which regulates relations between the two states.

The accord obliges Greece not to block the accession of its neighbour to international organisations.

British barrister and law professor Phillipe Sands, speaking for the Macedonian team, told the court that its judgement in the case would have a major impact on Macedonia's internal stability.

"Whilst the issue in the case may be discreet, the stakes are high. The case is about holding the respondent to its obligations under a bilateral treaty so that it is not allowed to object to the applicant [Macedonia] entry into NATO and other international organisations. The case is of evident significance for the country's internal stability and for the regional well-being," he said in court on Monday.

Professor Sean Murphy also spoke for the Macedonian side on Monday, offering background on Greece's "aggressive" opposition to Macedonia's membership in NATO.

"From 1995 to 2007 Macedonia undertook all the necesary steps on the road to admission to NATO. By 2007 it appeared likely that three countries would be invited to join NATO at the Bucharest Summit in 2008," he explained.

"However in 2007 and 2008, Greece engaged in a vigorous and systematic campaign in opposition to Macedonia's membership in NATO," Murphy continued.

He told the court that "this campaign was not subtle or discrete, it was a battle waged openly and aggresively".

Macedonia is to elaborate its arguments before the court on Monday and Tuesday, and Greece on Thursday and Friday.

The 15 ICJ judges, from all around the world, are expected to decide on this case within the next six months, or by the end of the year at the latest.

On March 28, Macedonia will respond to Greece’s defence and the hearing will conclude on March 30 with the final word from the Greek side.

“Macedonia will probably use statements from former Greek officials to back its case," Vasko Popetrevski, editor of the daily Dnevnik newspaper, told Balkan Insight.
 
He said that statements of former Greek prime minister Kostas Karamanlis and former foreign minister Dora Bakoyannis from before the 2008 NATO summit in Bucharest will show they did not allow Macedonia to join NATO because of Greek objections to the country's name.

“This may be taken by the ICJ as proof of the official stand of the country,” Popetrevski said.

Greece argues that Macedonia broke the 1995 accord by taking a hard line over the "name" issue and by "stealing" its history by renaming airports, highways and sport arenas after Ancient Greek heroes.

“Greece will try to prove that it is not exercising any veto against Macedonia joining NATO,” the Greek journalist and publicist Takis Michas told Balkan Insight.

He notes that the joint NATO communiqué issued after the 2008 Bucharest summit stated that the two countries had failed to reach a decision on Macedonia’s accession and did not mention a Greek veto.

Observers say they are unsure whether an ICJ verdict in favour of Macedonia would be applicable in reality. Macedonia wants Greece to withdraws its objections to Macedonia's NATO membership so that the country can join.

Established in 1945, the ICJ's main function is to settle legal disputes between states. ICJ rulings are final and cannot be appealed. However, the court has no instruments to make countries comply with rulings.

Macedonian diplomats close to the ICJ case say the outcome to the lawsuit should not be linked to the ongoing “name” talks between Macedonia and Greece, held under UN auspices.

The dispute is almost two decades' old. Greece insists that the name "Republic of Macedonia" implies a territorial claim to the Greek northern province, also called Macedonia.

In late 2009, Greek objections to Macedonia's name prevented the EU from extending a start date for Macedonia's accession talks with the block, despite a previous recommendation from the European Commission for negotiations to start.