The US Department of Justice has put in a request to detain supertanker Grace 1, which will be considered by Gibraltar's attorney general, Report informs citing the RIA Novosti.
The vessel, carrying Iranian oil, has been held off Gibraltar since 4 July.
It was set to be released within hours, after the attorney general indicated he would make no further order for its detention.
But, following a late US application, the matter has been adjourned until 16:00 BST.