* United Nations holds high-level summit on DRC crisis
* Rwanda says solution impossible if continues to be blamed
* U.N. summit calls for end to external support for rebels
Rwanda defiantly denied claims at the United Nations on Thursday that it was aiding rebels in Democratic Republic of Congo and rejected U.N. chief Ban Ki-moon's summary of a meeting on the crisis, diplomats said.
According to Ban, most states attending a high-level meeting on the sidelines of the U.N. General Assembly with Rwandan President Paul Kagame and Congolese President Joseph Kabila "condemned all forms of external support" to the rebels.
Kagame said after the meeting that Rwanda rejected allegations it was supporting the M23 rebels and said that "solving the crisis will be impossible if the international community continues to define the issue erroneously."
M23 rebels, who have ties to a warlord wanted by the International Criminal Court for war crimes, Bosco Ntaganda, have been fighting government soldiers in eastern Congo's North Kivu province since April. Some 320,000 civilians have been displaced.
"Most participants strongly condemned all forms of external support to the M23 and other negative forces in the DRC, and demanded the immediate and permanent cessation of such support," according to the meeting summary. "Some participants cautioned that those supporting the M23 could also be held accountable."
"They stressed ... the urgency of constructive engagement and dialogue between the DRC and Rwanda," it said.
Despite Rwanda's denials, a senior U.N. diplomat has said that privately Kigali was "a bit embarrassed, to say the least, and this could be one of the reasons behind the lull (in fighting) in the Kivu." He said if Rwanda withdrew support then the M23 group, numbering about 1,500, "could be subdued."
The DRC said last month it had asked the U.N. Security Council to place sanctions on Rwanda's defense minister and two top military officials for backing the rebellion.
A U.N. experts' report has accused Rwandan Defense Minister James Kaberebe, chief of defense staff Charles Kayonga, and General Jacques Nziza, a military adviser to President Paul Kagame, of being "in constant contact with M23."
"There can be no possible justification for such support, whether in terms of military hardware, or strategic advice. It must stop," Britain's Minister for Africa, Mark Simmonds, told the U.N. summit. "And there can be no impunity for those who violate human rights. They must be brought to justice."
France said it would support sanctions against M23 and warned neighboring states against supporting the group.
"The M23 is benefiting from external support, including from neighboring DRC states," said French Minister for the Francophone countries Yamina Benguigui. "Nothing can justify the support of an armed rebellion led by war criminals. All support of M23, whatever it is, must stop."
As uneasy neighbors, Congo and Rwanda have gone to war against each other in the past. Rwanda has backed armed movements in the DRC during the past two decades, citing a need to tackle Rwandan rebels operating out of Congo's eastern hills.
U.S. Secretary of State Hillary Clinton met jointly with Kagame and Kabila on Monday in New York and pressed them to resolve the conflict.
In July the United States withdrew some $200,000 in military aid for Rwanda, Washington's first direct punitive action against the Rwandans over the crisis. Several other western European nations also have cut or suspended aid.
The United Nations said it was working with east and central African states on their proposal for a neutral force to tackle the M23 and other armed groups in eastern Congo.
"It is something that generates interest, but we are short of a real concept of operations - who would be in, who would do what, who would pay - and this is why more work needs to be done," said U.N. peacekeeping chief Herve Ladsous after the meeting.
"We are already working (with them) to flesh out the concept because at the end of the day it will be submitted to the Security Council and the Security Council will want very precise explanations as to what it is all about," he said.
A resolution mandating military intervention in the DRC would have to be approved by the 15-member Security Council.
"Before endorsing any such support, we and the U.N. Security Council will want to understand the intended role and scope of the force," said Britain's Simmonds. Britain, the United States, France, China and Russia are veto-wielding council members.
A U.N. mission in the DRC, known as MONUSCO, has more than 17,000 troops, but the force is stretched thin across a nation the size of Western Europe and struggles to fulfill its current mandate of protecting civilians.
U.N. helicopter gunships frequently back up outgunned government forces, but even that firepower failed to prevent rebels from taking several towns in July. The U.N. force would work with any neutral force, but could not launch operations.