US Secretary of State John Kerry has arrived in the Austrian capital, Vienna, to join the ongoing Iran nuclear talks.
Kerry and his counterparts from Russia, China, France, Germany and the UK have been invited to attend the negotiations.
Britain, France and Germany said that they would send their foreign ministers to Vienna on Sunday.
However, Chinese and Russian foreign ministers will not attend the talks, sending lower-ranking officials instead.
The development comes as senior Iranian nuclear negotiator Abbas Araqchi said Iran and the six world powers have made relative progress over the text of a final nuclear deal, completing about 60-65 percent of the text.
Araqchi stated that there are still differences between the two sides over major issues.
He also warned that excessive demands by the other side may cause the talks to fail.
The Iranian official also expressed hope Kerry’s presence as well as other foreign ministers would help overcome remaining differences.
Ahead of Sunday talks, Iran’s Foreign Minister Mohammad Javad Zarif and US Deputy Secretary of State William Burns met in Vienna.
On July 3, Iran and the five permanent members of the UN Security Council – the United States, Russia, France, Britain and China - plus Germany formally kicked off their sixth round of talks this year in Vienna to discuss a permanent accord on Tehran’s nuclear energy program.
Iran and the six countries have been discussing ways to sort out differences and achieve a final deal that would end the decade-old dispute over Iran’s nuclear energy program.
The two sides sealed an interim deal in Geneva, Switzerland, on November 23, 2013. The deal came into force in January and expires on July 20, but can be extended depending on the agreement of all parties involved.
