European Union (EU) foreign ministers on Monday endorsed tougher sanctions over Iran's nuclear program, including measures to block oil and gas investment and curtail its refining and natural gas capability.

Foreign ministers from the 27 EU member states adopted a decision implementing the measures contained in UN Security Council Resolution 1929 as well as extra measures identified by EU heads of state and government at their June summit.

EU's restrictive measures, which went beyond UN sanctions imposed on June 10, followed a similar U.S. move.

The decision provides a comprehensive and robust package of sanctions in the areas of trade, financial services, energy, transport as well as additional designations for visa ban and asset freeze, in particular for Iranian banks, the Islamic Revolutionary Guard Corps and the Islamic Republic of Iran Shipping Lines.

Meanwhile, the EU foreign ministers reaffirmed the longstanding commitment to work for a diplomatic solution of the Iranian nuclear issue, calling on Iran to seize this opportunity to allay the concerns of the international community and agree on a concrete date for talks.

British Foreign Secretary William Hague said Britain has been in recent weeks seeking an agreement in the EU on a strong package of sanctions implementing the UN Security Council resolution. London also wanted a message to Iran that it can not just walk away from negotiations and expects no further pressure.

"And I hope Iran takes the message from that that the European nations are open to negotiation about the nuclear program but if they do not respond, we will intensify the pressure," Hague said.

Swedish Foreign Minister Carl Bildt said the Americans do not have much room to tighten their sanction as they have had sanctions since 1979.

"Now we (the EU) go some what beyond. That might have an effect," he told the press. "But without emphasizing and strengthening the diplomatic track, there is a risk of ending up with a dead end, which can be dangerous."

Acting Belgian Foreign Affairs Minister Steven Vanackere stressed that the EU position is "very balanced," as it is a "dual-track" position. "We want to be able to encourage Iran to come to the negotiation table, which can be the solution for the problems. At the same time, since it is a dual-track, if dialogue is not possible sanctions can be necessary and then they have to be balanced," he said.

"I think we came to an agreement on a position which is quite balanced," he added.

Meanwhile, Iran has reportedly submitted a letter to the International Atomic Energy Agency (IAEA) on resuming nuclear talks.

The letter, jointly provided by Iran's National Security Supreme Council and Iran's Atomic Energy Organization, expresses Iran's readiness to start uranium swap talks, Iranian satellite Press TV reported on Monday.

Earlier in the day, Iranian Foreign Ministry spokesman Ramin Mehmanparast said Iran is ready to start the nuclear talks "without delay," the semi-official ISNA news agency reported.