The EU does not consider halting sanctions off Iran, EU Foreign Policy chief Catherine Ashton's Chief Spokesperson Michael Mann said, the Guardian reported.
The talks started at 11am Moscow time (8am BST) with a plenary meeting between an Iranian delegation led by Saeed Jalili, the secretary of Iran's Supreme National Security Council, and a six-nation group of negotiators from the US, UK, France, Germany, Russia and China.
A spokesman for Catherine Ashton, the EU foreign policy chief who acts as convenor for the group, said it expected the Iranians to maintain a solid negotiating position.
The spokesman, Michael Mann, said: "As far as we are concerned, we have put forward a concrete set of proposals; the Iranians have raised a set of ideas and issues.
"Mr Jalili said on the phone last week that he was prepared to seriously engage with our proposals, so we want to hear what he says. We have to move forward at these talks ... There is no point in having talks for talks' sake."
Mann said the right to enrich uranium was not specifically mentioned in the Non-Proliferation Treaty, and that the UN security council has passed several resolutions calling on Iran to suspend enrichment until it has assured the international community of its peaceful intentions.
The Iranian team of negotiators headed by Supreme National Security Council (SNSC) Secretary Saeed Jalili is representing the Islamic Republic, while the six world powers are led by EU foreign policy Chief Catherine Ashton.
Prior to the Moscow meeting, Iran and the 5+1 group held nuclear talks in Istanbul on April 14, and in Baghdad on May 23.
The West suspects Iran is trying to develop atomic bombs, while Iran says its nuclear work is solely for civilian purposes.
Iran has repeatedly dismissed the Western allegations, arguing that as a signatory to the nuclear Non-Proliferation Treaty (NPT) and member of the International Atomic Energy Agency (IAEA), it has every right to pursue nuclear technology for peaceful purposes.
Edited by: S. Isayev