Turkey's foreign minister raised concerns on Monday about Iran or the United States proposing any new regulations for transiting the Strait of Hormuz, and said he saw difficulties around proposals to re-open the waterway with an international force.

Foreign Minister Hakan Fidan - who is in close touch with the U.S., Iran and mediator Pakistan - said in comments reported by state-owned Anadolu Agency that Hormuz should be opened through diplomacy, after weekend U.S.-Iran talks failed to reach a deal to end the war.

Negotiators should use "convincing methods" in talks with Iran and Hormuz should be opened as soon as possible, he said, adding that "nobody wants" the strait to become part of the war.

"There are many difficulties to intervening here with an international armed force. Especially as the war continues, how much will it narrow, expand? We see many countries are not keen on this," Fidan said.

"The problem is whether there will be proposals on new regulations from now on, particularly from Iran," which could decide to be "more active" on the strait, he added.

In retaliation for U.S.-Israeli attacks, Iran effectively closed Hormuz, through which about a fifth of global energy supplies transit, sending energy prices soaring.

Starting on Monday, the U.S. military said it would begin a blockade of all maritime traffic entering and exiting Iranian ports and coastal areas. Washington has sought help to re-open the strait from allies, who have not expressed interest.

Fidan said the U.S. and Iran were "sincere" in their ceasefire talks, but added that they could encounter problems if they approached the issue of Iranian nuclear enrichment from an "all-or-nothing" perspective.

A source said Fidan spoke on Sunday with U.S. and Pakistani officials involved in the talks.

-Reporting by Tuvan Gumrukcu; Writing by Jonathan Spicer; Editing by Aidan Lewis/Reuters