The European Union has condemned the expulsion of two EU diplomats from Ethiopia as "totally unacceptable".
The EU cut aid after last year's election violence
The two were deported after being caught allegedly trying to smuggle two fugitives into Kenya.
These include an Ethiopian lawyer who worked for the European Commission. Ethiopia said they were arrested over "serious crimes" without specifying.
The expulsions come at a time of strong international criticism of Ethiopia over last year's disputed elections.
The EU halted budgetary aid to Ethiopia in the wake of the poll and the wave of violence that followed it.
Until the election violence, Ethiopian Prime Minister Meles Zenawi had been seen as part of a "new generation" of African leaders.
The chief observer for the EU during the elections, Ana Gomes, on Thursday said a leaked report into an alleged "massacre" confirmed that the government did not respect human rights.
An EC official, who did not wish to be named, told the BBC he was very concerned about lawyer Yalemzewd Bekele, following her arrest.
Human rights group Amnesty International says she is at a high risk of being tortured.
The identity of the person arrested with the lawyer has not been revealed but they did not work for the EC, the official said.
Swedish diplomat Bjorn Jonsson and Italian EU official Enrico Sborgi were deported on Thursday night.
The arrests were made after a car with diplomatic number plates was stopped near the southern border town of Moyale, Ethiopian officials say.
Amnesty says it believes Ms Yalemzewd was arrested in connection with the publication and distribution of a calendar of action for non-violent civil disobedience by the opposition party Coalition for Unity and Democracy (CUD).
CUD was in the forefront of protests over last May's elections, saying it was cheated of victory.
Several CUD leaders are on trial on a number of charges, including one of trying to overthrow the government.
Almost 200 people were killed when the police put down the protests, a leaked report said this week.
Development Commissioner Louis Michel said he had called Ethiopia's envoy in Brussels for an explanation.
"There will be repercussions," he said.
He also said he had been trying since Thursday to contact Mr Meles about the incident, without success.
"Usually I can make contact quite easily with Prime Minister Meles," he said.
A statement from Ethiopia's interior ministry said the attempt to take the Ethiopians out of the country "violates the sovereignty of the country while jeopardising the security of the nation".
"Any international organisation operating in Ethiopia needs to respect the laws of the host country and face punishment if it violates the law," the statement added.