European Union's Foreign Policy Chief Catherine Ashton (L) and Turkish Foreign Minister Ahmet Davutoglu arrive prior to a meeting in Istanbul on April 14, 2012.
Hours after the completion of the first round of new talks between Iran and the P5+1 - the US, Britain, Russia, China, and France plus Germany- the two sides started the second round of comprehensive negotiations in Istanbul.
The first round of negotiations was held on Saturday morning after which Iran started bilateral talks with the members of the P5+1 minus the US.
Sources close to the Iranian delegation said Iranian negotiators have rejected multiple requests from US for bilateral negotiations both after the first round of talks and before the beginning of the second round.
Meanwhile, the EU foreign policy chief, Catherine Ashton, has met three times with Secretary of Iran's Supreme National Security Council Saeed Jalili over the past 24 hours.
Following the first round of talks, EU sources said the general atmosphere of talks was positive, but Iranian sources said it was too early to judge whether the atmosphere of the discussions has been positive before hearing the viewpoints of all sides.
The Iranian delegation present at the talks is headed by SNSC Secretary Jalili while the delegations of the six world powers are headed by EU foreign policy chief Catherine Ashton.
Tehran and the P5+1 have already held two rounds of talks in the past, one in Geneva in December 2010 and another in Istanbul in January 2011.
The second round of the new negotiations will be held in the Iraqi capital of Baghdad, the date of which will be announced at the end of the Istanbul meeting.