Japanese Prime Minister Shigeru Ishiba is planning to cancel his attendance at the North Atlantic Treaty Organisation (NATO) summit in the Hague, a source with direct knowledge said on Monday.

The US was one of the parties to the 2015 nuclear deal in which Iran agreed to limits on its uranium enrichment program in exchange for sanctions relief and other benefits.

The United States and Iran remain in contact over the resumption of talks on Tehran's nuclear program, but no formal negotiations are planned, officials from both sides said on June 26.