Rwanda angry over London arrest of spy chief Karenzi Karake.

The genocide had a huge impact on Rwanda and its neighbouring countries

The Rwandan government has branded the arrest of its intelligence chief Karenzi Karake as "an outrage".

Gen Karake, 54, was arrested at Heathrow Airport on Saturday, accused of ordering massacres in the wake of the 1994 Rwanda genocide.

He was arrested by Met police officers under the European Arrest Warrant on behalf of the Spanish authorities.

Williams Nkurunziza, Rwanda's High Commissioner to the UK, said it was "an insult to our collective conscience".

Prime Minister David Cameron's official spokeswoman said it was an "operational matter" for the police who were legally obliged to act on valid European Arrest Warrants.

Louise Mushikiwabo, Rwanda's foreign minister, called the arrest "an outrage"adding: "Western solidarity in demeaning Africans is unacceptable".

Andrew Mitchell, former international development secretary, said he believed the arrest was a "reprehensible abuse" of the law.

'Contested vigorously'

In 2008, Spanish investigative judge Andreu Merelles indicted Gen Karake for alleged war crimes along with 39 other current or former high-ranking Rwandan military officials.

He is also accused of ordering the killing in 1997 of three Spanish nationals working for Medicos del Mundo.

But the Rwandan government is said to be puzzled by the timing of Gen Karake's arrest, as he has travelled to the UK several times since the indictment was issued.

Mr Nkurunziza told the BBC World Service: "We take strong exception to the suggestion that he's being arrested on war crimes.

"Any suggestion that any of our 40 leaders are guilty of crimes against humanity is an insult to our collective conscience."

Gen Karake was remanded in custody after appearing at Westminster magistrates court and he will reappear on Thursday.

A spokesman for Spain's National Court said it was now up to the British authorities to decide whether or not to extradite him.

Arrest strains fragile UK-Rwanda relations

There are numerous memorials around Rwanda to those killed in the genocide

By BBC foreign correspondent Karen Allen

The arrest of General Karenzi Karake in London is bound to strain what is increasingly becoming a fragile relationship between Britain and Rwanda.

Like two best friends, harsh words are exchanged from time to time, but on this occasion it feels like a smart slap whose sting may last for some time.

It is perhaps not surprising that the detention of Rwanda's head of intelligence is being flagged up by London as a European "obligation" rather than a British decision.

There is a strong ambition in Whitehall that the matter simply goes away. After all it was a Spanish high court judge that made the accusation of war crimes, not a British one.

Read more from Karen here.

Mr Mitchell told the BBC he thought the arrest was "completely wrong".

"It's being used by supporters of the genocidal regime against those who stopped the genocide.

"I think it is reprehensible that the European Arrest Warrant is being abused in this way by a junior Spanish judge," he said. "It's being used for political reasons and not judicial ones."

He added that he agreed with American officials who have described the indictments as "un-researched, politically motivated and lacking in facts".

Phil Clark, lecturer on Africa's Great Lakes Region at the School of Oriental and African Studies in London, said there were concerns about the evidence in the Spanish indictment.

"There's a sloppiness I think in much of the investigation that underpins this and even very critical human rights groups, that have tended not to be very friendly to Rwanda in the past, have raised questions about the quality of the Spanish arrest warrants."

Rwanda reacts

By Mary Harper, BBC World Service Africa editor

Rwanda's furious reaction to the arrest is typical.

Whenever it is criticised, especially in relation to reprisal killings of Hutus, it lashes out, accusing its critics of "genocide denial".

In some ways, it seeks to exploit the collective international guilt arising from the world's failure to stop the genocide of 1994.

Britain finds itself in a difficult position. It has been a close friend of Rwanda, praising the government of Paul Kagame for turning the country around and becoming one of Africa's economic "success stories".

However, the Kagame government comes down hard on dissent, stifles media freedom, and has been accused of meddling in conflicts across its borders.