The European Union warned Iran on Sunday that it risks new sanctions if it fails to return to international talks aimed at easing concerns about its disputed nuclear programme.

In conclusions adopted at an EU summit, the council of 27 EU states "urges Iran to respect all obligations under international law."

"It expresses its continued concern over the expansion of Iran's nuclear and missile programmes, in violation of UNSC (UN Security Council) and IAEA (International Atomic Energy Agency) Resolutions," it said.

EU leaders also voiced worries about Iran's "lack of cooperation with the IAEA in addressing outstanding issues, including those pointing to possible military dimensions to its nuclear programme."

Talks between Iran and the so-called E3+3 -- Britain, France, Germany, Russia, China and the United States -- have hit a dead-end as Tehran refuses to meet international demands to freeze its dispute atomic programme.

"We urge Iran to enter into constructive and substantial talks with the E3+3 in a way to arrive at a comprehensive, negotiated, long-term solution of the nuclear question in order to avoid possible further restrictive measures," EU leaders said.

At the same time, EU leaders said they were asking their foreign ministers "to prepare new restrictive measures to be decided upon and to be implemented at the appropriate moment in the case that Iran continues not to cooperate seriously nor to meet its obligations."

The European leaders reiterated the "commitment of the European Union to work for a diplomatic solution of this issue."

The United Nations, the United States and the EU have already imposed a raft of sanctions against Iran since 2007 over its refusal to halt uranium enrichment activities.

EU leaders voiced satisfaction over new sanctions imposed by the 27-nation bloc over Iran's "unacceptable human rights violations" and measures against five Iranians in connection with a foiled plot to assassinate the Saudi ambassador to the United States.