"According to information provided to the state TV correspondent by a person close to the negotiating team, another round of negotiations will likely be held tonight or tomorrow," state broadcaster IRIB reported.

The trilateral direct negotiations were taking place with host Pakistan, a senior White House official said earlier Saturday, a departure from recent practice where both sides held talks via a mediator while seated in separate rooms.

An Iranian state TV correspondent reported that there were "plans for a third round of talks", the latest in the efforts mediated by Pakistan to end the war.

"We are waiting to see whether this (the third round) will happen or not," the correspondent said, according to state TV.

Iranian news agency Tasnim reported that the issue of the strategic Strait of Hormuz -- through which nearly global crude oil and liquefied natural gas passes in peacetime -- was "one of the topics that faces serious disagreement" among the negotiators.

The reports came as the White House said high-level in-person trilateral talks with Iran and Pakistan were "ongoing" in Islamabad late on Saturday.

A senior White House official said in a brief statement that the talks were continuing.