Iran on Monday called off talks between Tehran and Washington aimed at improving security in Iraq, describing the dialogue as meaningless.

A statement by the Iranian foreign ministry, in effect, puts on hold any meetings between the two countries, which last year held three rounds of talks in Baghdad, easing a diplomatic freeze dating back almost three ­decades.

Mohammad Ali Hosseini, an Iranian foreign ministry spokesman, said that continuing talks with the US over Iraqi security “makes no sense” so long as the US ­military was attacking residential areas in Sadr City, a neighbourhood in Baghdad that is a stronghold of the Mahdi army, a Shia militia.

“The focus of discussions with the US is Iraq’s security and stability. We are witnessing indiscriminate bombardment of Iraqi residential areas by the US occupying forces,” Mr Hosseini was quoted by Iran’s IRNA press agency as saying.

“Given the current circumstances, holding the next round of talks [with the US] would have no result and makes no sense,” he said.

In a sign of deteriorating relations between Iran and Iraq, an Iraqi official said that security forces had discovered Iranian-made weapons inside Iraq and that Baghdad would investigate how they arrived there.

The statement came two days after an Iraqi delegation returned empty-handed from a visit to Iran.

The officials met Ghassan Soleimani, a general in the Iranian Revolutionary Guard’s elite Quds Force, who has been accused by the US of direct responsibility for channelling support to Iraqi Shia militia splinter groups.

Baghdad appears to be trying to pin down Iranian ­officials on allegations of support for the Shia militias, but Tehran appears unwilling to back away from its steadfast denials.

The diplomatic exchange is typical of the complexity of the relationship between Iraq’s highly fractured Shia-led government and Iran’s similarly byzantine state apparatus.

While the Iraqi government appreciates the diplomatic support lent to it by Iranian leaders and diplomats, particularly when compared to its Sunni Arab neighbours, many in Baghdad have expressed concern that the Iranian security services have cultivated ­client networks within radical Shia movements.

Until recently, however, Iraqi officials had generally avoided too specific an endorsement of US allegations that the Quds Force was backing radical splinter groups of the Mahdi army which have attacked both US forces and Iraqi security forces.

Ali al-Dabbagh, an Iraqi government spokesman, however, said that Iraq would investigate the Iranian support.

“The proof we have is weapons which are shown to be made in Iran. We want to trace back how they reached [Iraq], who is using them, where are they getting it,” Mr Dabbagh told Reuters.

“The Iraqi government will follow up with the Iranians and put [these findings] in front of them.”

Mr Dabbagh had previously said that there was “no conclusive evidence” of such support.