David Cameron has said the UK “cannot ignore the evidence” of Rwanda’s involvement with militia who have taken control of parts of the neighbouring Democratic Republic of Congo (DRC).
The prime minister has urged Rwandan president Paul Kagame to show he has “no links” to the M23 group of rebels.
A UN report published on Thursday accused Rwanda of backing the group.
The UK has said it will consider its “compelling” findings before deciding whether to give more aid to Rwanda.
The M23 have rejected calls to withdraw from Goma, the main city in eastern DRC, which they seized control of a week ago.
In separate phone calls to Mr Kagame and DRC leader Joseph Kabila, Mr Cameron urged them to ensure a communique by regional leaders condemning the M23 and urging them to withdraw from Goma was “translated into action”.
No 10 said Mr Cameron – who is in Brussels for a EU summit – made clear to Mr Kagame that “the international community could not ignore evidence of Rwandan involvement with the M23” and Rwanda’s leader must “show the government of Rwanda had no links to the M23”.
The UK is facing calls to suspend its aid programme to Rwanda until its leaders disassociate themselves from the M23 and demonstrate that they are not offering the rebels any practical support.
The former international development secretary Andrew Mitchell controversially approved a £16m tranche of financial aid for Rwanda on his last day in the job in September – at a time when several other EU nations had suspended their programmes.
His successor, Justine Greening, has said she will think “very carefully” before sanctioning any further financial support to Rwanda – starting with a decision next month on a further £11m.
Reacting to the UN’s report, Ms Greening and Foreign Secretary William Hague said all external support for the M23 was “unacceptable”.
“We judge the overall body of evidence of Rwandan involvement with M23 in the DRC to be credible and compelling,” they said in a joint statement.
“We will be studying the implications of this report in full, but these allegations will necessarily be a key factor in future aid decisions to the government of Rwanda.”