Rwanda refused formal requests to assist a British police investigation into genocide suspects living in the UK, the BBC has been told.
The Crown Prosecution Service (CPS) has revealed in 2010 it asked for what is known as "mutual legal assistance" to help the Metropolitan Police.
A UK resident accused of genocide anywhere in the world since 1991 can be put on trial in Britain.
Rwanda's high commissioner to the UK says they are working with the CPS.
Williams Nkurunziza told the BBC: "Why would the UK or anyone who is interested in the delivery of justice be interested in trying genocide suspects in the UK? The people that desire to see justice being done are not in the UK, they are in Rwanda".
Around 800,000 ethnic Tutsis and moderate Hutus were killed in Rwanda in 1994.
In 2009 Rwanda sought to extradite four men living in the UK who it claimed had been involved in the genocide.
The UK High Court refused, ruling that if Dr Vincent Brown; Charles Munyaneza; Celestin Ugirashebuja; and Emmanuel Nteziryayo were returned to Rwanda, there would be "a real risk" they would suffer "a flagrant denial of justice".
The following year, the law was amended to allow suspects to be prosecuted in Britain.
The CPS says it contacted the Rwandan Government about the four men on behalf of Counter Terrorism Command at the Metropolitan Police.
It says: "The specific allegation being investigated in this case was genocide."
An application for "mutual legal assistance" in a case like this would usually mean a request for evidence.
The CPS told the BBC: "The timing, nature and scope of the request were based upon the police investigation."
According to the CPS, the Rwandan government rejected all four applications.
Mr Nkurunziza told the BBC he is only aware of two such requests.
He said his country is currently working with the CPS in a renewed attempt to extradite those it suspects of being involved in the genocide.
Earlier this year the same four men and a fifth suspect, Celestin Mutabaruka, were arrested and face a full extradition hearing in March 2014.
The High Court heard in 2009 that the four men deny being involved in the genocide and it is understood Mr Mutabaruka also denies the allegations against him.
Mr Nkurunziza says Rwanda has reformed its legal system and its prisons and added: "The ICTR (International Criminal Tribunal for Rwanda) has transferred cases to Rwanda for trial. Countries like Norway and Canada have extradited people back to Rwanda to stand trial and I believe UK should be able to hold the same view."
He dismisses concerns from Human Rights Watch that a fair trial cannot be guaranteed and that the judiciary in Rwanda is not independent. He says the views of countries which have "assessed the system... carry greater weight than Human Rights Watch".
One of the five men Rwanda is trying to extradite is Dr Vincent Brown, known originally as Vincent Bajinya. He told BBC Radio 4's PM Programme: "There's no fair trial in Rwanda."
He says he denies the allegations against him and wants to clear his name: "I am prepared to face any fair trial anywhere in the world - anywhere else where I can get it."
He says he had hoped he could face a trial in Britain.
"I wrote so many letters to the Crown Prosecution Service in this country. I wrote letters to the British police asking them to investigate me. I was willing to collaborate with the police. But nothing has happened," he said.
There have been trials of genocide suspects in Germany, Canada and the Netherlands but Rwanda's High Commissioner says trials should take place where the crimes were committed.
Mr Nkurunziza says: "Our view is all genocide suspects, wherever they are, should be tried in Rwanda."
A spokesman from the Crown Prosecution Service told the BBC: "There is no current domestic investigation into alleged war crimes committed by Vincent Bajinya and others. Without an investigation in the UK, a domestic prosecution cannot take place.
"All of the evidence in this case is with the Rwandan authorities and they have requested extradition. CPS prosecutors are now acting on behalf of the Rwandan authorities in these proceedings under the normal rules for extradition matters."
The Metropolitan Police declined to comment.