UK Prime Minister Boris Johnson's spokesman called the arrest an 'unacceptable breach' of the Vienna Convention. The envoy was held after attending a vigil for the victims of the Ukrainian airliner disaster.
Britain has summoned the Iranian ambassador to protest the arrest of its envoy to Tehran on Saturday, the government said Monday.
"This was an unacceptable breach of the Vienna Convention and it needs to be investigated," Prime Minister Boris Johnson's official spokesman said on Monday.
"We are seeking full assurances from the Iranian government that this will never happen again."
The British ambassador to Iran, Rob Macaire, was briefly detained on Saturday night after attending a vigil for the victims of the Ukraine International Airlines disaster. He left the vigil when people began to demonstrate, but was later accused of helping to organize the protest.
lc/rt (AFP, Reuters)