* Mines minister says writes U.S. SEC chief seeking help
* Congo accuses Rwanda of funding revolt in country's east
KINSHASA, Sept 18 (Reuters) - The Democratic Republic of Congo is seeking an embargo on trade in minerals from Rwanda, which it accuses of funding a rebellion in the country's east, according to a letter written by the mines minister and seen by Reuters on Tuesday.
Tensions between the neighbouring central African countries have risen sharply this year over allegations made by U.N. experts that Rwanda is supporting the uprising in the Congolese province of North Kivu, charges denied by Kigali.
In a letter dated Aug. 29 to Mary Shapiro, president of the U.S. Securities and Exchange Commission, Congo's mines minister accused Rwanda of helping armed groups smuggle minerals out of Congo and into Rwanda for export.
"To put an end to this situation, one of the solutions would be to impose an embargo on all minerals coming from Rwanda, until the establishment of a lasting peace in the provinces of North and South Kivu," Martin Kabwelulu said in the letter.
"It is in this context that your institution ... is invited to instruct all American companies ... to no longer buy minerals extracted and/or coming from Rwanda," he said.
An official at the SEC, which has no jurisdiction to impose trade embargoes, said he was not aware of the letter.
Kabwelulu wrote another letter on the same date to ITRI, a British-based tin industry organisation, calling on it to suspend its work helping to monitor certification of conflict-free tin in Rwanda.
An official at ITRI said it was consulting partners on the matter and would respond directly to Congo's mines ministry "in due course".
The Rwandan government did not respond to emails and telephone calls asking for comment on Tuesday but it has repeatedly pledged to clean up its mineral sector and support new traceability initiatives.
Rights groups have long said that illegal exploitation of Congolese minerals such as tin, tungsten, tantalum and gold has helped fuel nearly two decades of conflict in the east of the vast country that has left millions dead.
There has been growing international focus on efforts to tackle so-called "conflict minerals" and last month the SEC confirmed rules which will require U.S. companies buying minerals from Congo or its nine neighbours to demonstrate that the financial proceeds have not contributed to fighting.
Congo and Rwanda had been working closely on the issue before allegations of Rwandan complicity in the M23 rebellion brought about a breakdown in relations.
Rwanda has historically benefited from the exploitation of hundreds of millions of dollars of Congolese minerals.
A U.N. report in December last year said that Bosco Ntaganda, one of the leaders of the current M23 rebellion who is also wanted by the International Criminal Court for war crimes, was continuing to smuggle minerals through Rwanda.
On Tuesday the advocacy group Global Witness said that its research indicated Rwanda was continuing to launder proceeds from minerals that may have benefited armed groups.
"Not only does Rwanda's predatory behaviour jeopardise its own reputation, ... it also risks undermining the credibility of initiatives being developed to tackle the conflict minerals trade," Global Witness spokeswoman Annie Dunnebacke said.
Last year Rwanda returned to Congo more than 80 tonnes of smuggled minerals that had been seized by customs officials.