A senior Chinese envoy on Monday urged Iran and world powers to quickly resume stalled talks over Tehran's suspect nuclear programme, and called for better cooperation between the Islamic state and the UN nuclear watchdog.

Assistant foreign minister Ma Zhaoxu made the appeals at the end of a two-day visit to Tehran during which he spoke with Iran's deputy nuclear negotiator Ali Bagheri, Iranian state television reported.

Ma's trip came amid heightened tensions between the West and Iran over Tehran's nuclear activities, which the United States and its allies fear masks a drive for atomic weapons.

Increased Western economic sanctions on Iran in recent weeks and months have unsettled China, which is the biggest customer for Iranian oil.

Beijing has refused to follow a US and EU embargo on Iranian oil, though last month it reduced the amount it was importing, and it has held talks with other suppliers such as Saudi Arabia.

"It is now necessary for negotiations between Iran and the 5+1 group (Britain, China, France, Germany, Russia and the United States) to resume as rapidly as possible, and for cooperation to be reinforced between the International Atomic Energy Agency and Iran and for both sides to find effective solutions to resolve their problems," Ma said.

State television said the Chinese diplomat also expressed hope that Iran's chief negotiator, Saeed Jalili, would "send as soon as possible" a reply to an EU letter sent nearly four months ago opening the door to resuming the talks between Iran and the 5+1 group.

"The Iranian side said that Mr Jalili was soon going to send his response to the letter" from EU foreign policy chief Catherine Ashton, he said. "I think this is a positive signal from Iran."

Bagheri was quoted as saying that Iran rejects the West's "approach of dialogue and pressure, which leads to failure and an impasse."

He said Iran wanted talks with world powers based on "dialogue and cooperation".

Iran denies any military dimension to its nuclear programme, insisting it is purely for civilian uses.

The IAEA, though, in November issued a report saying Iran was engaged in activities that strongly suggested it was researching an atomic weapon and the capacity to put a nuclear warhead on a ballistic missile.

Israel, which views a nuclear-armed Iran as a threat to its survival, has warned it could attack Iranian nuclear sites.

The United States has not gone as far, though it maintains that "all options are on the table" in dealing with Iran.