Iran's President Hassan Rouhani travelled to Russia to take part in the fourth summit of the Caspian Sea littoral states.
Rouhani headed to the Russian city of Astrakhan on Sunday to participate in the summit set for Monday after he wrapped up his visit to New York where he addressed the 69th annual session of the United Nations General Assembly.
Iran, Russia, Kazakhstan, the Republic of Azerbaijan and Turkmenistan are the five littoral states of the Caspian Sea.
The last meeting of the Caspian Sea littoral states was held in Azerbaijan capital Baku in November 2010.
The Caspian Sea is the largest enclosed body of water by area, and is variously classed as the world's largest lake or a full-fledged sea.
The issue of the Caspian Sea's legal regime has gained importance following the breakup of the Union of Soviet Socialist Republics (USSR) and the emergence of newly independent states.
Iran and six world powers—the United States, France, Britain, Russia, China and Germany—are currently in talks to work out a final agreement aimed at ending the longstanding dispute over Tehran's civilian nuclear energy program within a November 24 deadline.
Meanwhile, Iranian Foreign Minister Mohammad Javad Zarif described the talks as "serious, intense and very frank".
"Time is short, but issues are not that difficult to resolve," Zarif told reporters in New York on Friday. "Everything is very far and very close, it depends on how you look at it and what time of the day you start looking at this question. We are still apart, there are still quite a bit of differences on all these issues."
Last November, the two sides clinched an interim nuclear accord, which went into effect on January 20 and expired six months later. However, they agreed to extend their talks until November 24 as they remained split on a number of key issues.
The Iranian foreign minister said the next round of Tehran's nuclear talks with six world powers will be held in Europe.
"It will take place in Europe because New York is too far away," ITAR-TASS news agency quoted Zarif as saying after a Saturday closed-door meeting with his Russian counterpart Sergei Lavrov in New York.
He pointed to major differences between the two sides and underlined the need for the continuation of consultations.
Zarif reaffirmed Tehran's determination to seize the existing opportunity till the expiration of Iran's interim nuclear deal in November and noted that the existing issues are not too complicated to be resolved.
Need to continue talks
Zarif and his Russian counterpart held talks to discuss the progress of Tehran's nuclear talks.
During the meeting, the two top diplomats emphasized the need for the continuation of nuclear discussions between Iran and the six world powers.
Zarif and Lavrov also held talks on the upcoming summit of the Caspian Sea littoral states, which is scheduled to be held in the southern Russian city of Astrakhan on Monday.
Talks between Zarif and Lavrov were held as Iran and the six powers wrapped their latest round of closed-door talks in New York on Saturday.