Melbana Energy (ASX:MAY) has delayed drilling of its Amistad-11 well in Cuba after partner Sonangol failed to meet cash call obligations, according to a Friday filing with the Australian bourse.

The company operates the block 9 production sharing contract onshore in Cuba, holding a 30% interest, while the remaining 70% is owned by Sonangol, per the filing.

Despite mobilizing the rig to pad 1 and securing final permits in late November, Sonangol has stated it cannot provide additional funds this year and has requested that drilling be delayed until 2026, the filing said.

The company has demobilized personnel and equipment and issued a notice of default to Sonangol for unpaid cash calls, with failure to remedy the default within 60 days potentially forcing Sonangol to transfer its block 9 interest to Melbana, the filing added.

The company's shares plunged around 25% in recent Friday trade.