Six Iranians held in a US military raid in northern Iraq were working there with the approval of the authorities, Iraq's foreign minister has said.
The outside of the Iranian liaison office raided by US forces
The Iranian liaison office in Irbil did not yet have full consular diplomatic status but it had been operating for years, Hoshyar Zebari said.
The US said it believed the six people seized in Thursday's raid had targeted Iraqi and US-led coalition forces.
Russia said the raid was "unacceptable" and a violation of international law.
"It is absolutely unacceptable for troops to storm the consular offices of a foreign state on the territory of another state," Russian foreign ministry spokesman Mikhail Kamynin said.
"It is also not clear how this fits in with American statements that Washington respects the sovereignty of Iraq," he said.
Iraq's foreign minister said details of the detainees had been passed to the Americans.
"We contacted the US embassy and submitted all the information available to us on the nature of their work and the place of their work," he said.
"They have been working under the approval of the government."
One of the group, seized when US troops stormed the building, has since been released. Mr Zebari said the other five remained in US custody.
The troops raided the building at about 0300 (0001GMT), taking away computers and papers, according to local media.
AFP news agency quoted Pentagon spokesman Bryan Whitman as saying he did not know the nationality of the six but said they were "suspected of being closely tied to activities targeting Iraq and coalition forces".
The US is adamant that the building did not have diplomatic status.
However, Tehran said the attack violated all international conventions. It has summoned ambassadors from Switzerland - representing US interests - and Iraq.
A spokesman for Iran's foreign ministry described the raid as an attempt to sabotage Tehran's relations with Iraq. One Iranian MP said it showed America's cruelty and meanness.
The raid comes amid high Iran-US tension.
In a major speech on Wednesday, President George W Bush said the US would take a tough stance towards Iran and Syria, whom he accused of destabilising Iraq.
BBC diplomatic correspondent Jonathan Marcus says the raid could signal a ratcheting up of pressure on the Iranians, in line with the rhetorical thrust of his speech.
The US also accuses Iran of seeking nuclear arms. Iran denies both charges.
Tehran counters that US military involvement in the Middle East endangers the whole region.
In December, US troops detained a number of Iranians in Iraq, including two with diplomatic immunity who were later released.