Iranian top nuclear negotiator Saeed Jalili answered Ashton's letter, saying the country welcomes P5+1 return to talks.
Iranian Supreme National Security Council Secretary Saeed Jalili in a letter to the European Union Foreign Policy Chief Catherine Ashton welcomed P5+1 return to the table of negotiations, ISNA reported.
"Will of nations will replace tyrannical relations in the international system," Jalili said in the letter.
"Vein insistence of some governments on continuous unequal relations in the world and confrontation against nations' demands cannot last longer," he added.
The letter submitted to Ashton by Iranian ambassador to the EU reiterated that, "developments over past months showed that Iran's package of proposals put forward three years ago has been based on a truth understanding of realities."
He stressed respecting nations' rights and avoiding pressures as two fundamentals for bilateral cooperation.
Ashton, in a letter sent in early February following January talks in Istanbul, reiterated the group's position on Iran's nuclear issue.
She also affirmed that the world powers were keen to continue talks with Iran without any preconditions.
In Brussels, the EU said Ashton had written to Iran's chief nuclear talks negotiator, Saeed Jalili, offering a resumption of talks following talks in Turkey.
Iran and representatives of the five permanent members of the UN Security Council plus Germany as well as Ashton met in Istanbul on 21-22 January.
The EU's foreign policy chief said the six world powers are 'disappointed' as the two-day nuclear talks with Iran have ended with no breakthrough.