"We were authorised to issue one billion euros of bonds," the ILNA news agency quoted the deputy head of the state-owned National Iranian Oil Company, Hojatollah Ghamini-Fard, as saying.
He added: "250 billion euros were issued and the rest will be issued next Monday."
Ghamini-Fard said that "euro bonds worth five billion will be issued" next Iranian year which begins on March 21, 2011.
"Of this amount three billion euros will be allocated to the South Pars (gas field) and the rest will go to oil fields," he said, adding that bonds denominated in Iranian rials worth about three billion dollars will also be issued "in the near future."
He did not say which institution will be issuing the bonds but Iran said in February that its Bank Mellat, which is under US sanctions for allegedly financing weapons proliferation, would issue bonds worth one billion euros to develop gas fields.
Iran's economy minister Shamseddin Hosseini said then the bonds, with a three year lock-in period, will carry interest of eight percent and that the National Iranian Oil Company would act as "guarantor" for the bond issue.
Iran, which has the world's second largest natural gas reserves after Russia, had previously said it plans to invest 85 billion dollars within a decade to bolster gas exports.
While Iran sits on top of huge gas reserves, it imports as much of it from Turkmenistan as it exports to Turkey and has a long way to go to become a significant exporter.
The development of Iranian gas exports has been hampered by a lack of investment in production and growth in domestic consumption.
Western governments have put pressure on international firms to cut ties with Iran in a bid to pressure it to freeze a uranium enrichment programme the West believes is aimed at producing atomic weapons.
Iran says it wants nuclear energy purely for peaceful purposes.
