TEHRAN - Iranian foreign ministry said Sunday that its ambassador to London, called home after a former Iranian envoy to Argentina was arrested in Britain, was returning to his post but warned relations would only worsen unless the detained former diplomat was released.

Foreign ministry spokesman Hamid Reza Asefi said ambassador Morteza Sarmadi left for London Sunday after "consultations" over last month's detention of former Iranian ambassador to Argentina Hadi Soleimanpur.

Soleimanpur was arrested in northeast England on an extradition request from Buenos Aires accusing him of taking part in a 1994 bombing of a Jewish centre that killed 85 people.

"The arrest of an ex-ambassador is unacceptable for the Islamic Republic of Iran. We have conveyed the British side of the destructive effect it has. Political channels are still open," Asefi told reporters here.

"With his unconditional freeing, these destructive effects can be stopped," he added, saying Iranian Foreign Minister Kamal Kharazi and British Foreign Secretary Jack Straw were "in constant contact with each other".

Asefi insisted that Soleimanpur was "absolutely innocent".

"The accusations are absolutely baseless. The Islamic republic of Iran cannot sit silent," he said.

Relations between Britain and Iran have hit a low over the arrest of the former ambassador, which was followed by a gun attack on the British embassy in Tehran and sparked the indefinite closure of the mission.

Press attache of the British Embassy in Tehran Green Stock Saturday rejected reports that Ambassador Richard Dalton has left Iran.

The Persian-language daily Jam-e Jam quoted Stock as terming the reports as baseless.

The British media reported on Tuesday that Dalton had returned to London, IRNA reported.

He further said the British ambassador was scheduled to leave for London but had cancelled his trip for some reasons. Stock did not further elaborate.

Turning to the activities of various departments of the embassy after the Wednesday shooting, the attache said the political department of the embassy is currently active.

"It is not clear yet when the embassy would officially resume its work. We are waiting for our government to decide on the reopening of the embassy in Tehran," Stock said.

He said a number of non-essential staff of the embassy have left Iran but declined to give the exact number.