WASHINGTON, March 30 (Reuters) - The U.S. Treasury Department, weighing into international efforts to quell fighting in Congo and stabilize the central African state, on Friday announced sanctions against companies and individuals for supplying arms and money to warring militias.

The department said it was prohibiting Americans from doing business with seven firms and three individuals, which include the holdings of two Congolese gold dealers, Kambale Kisoni and Dieudonne Ozia Mazio.

The action also freezes any assets they may have under U.S. jurisdiction.

The Treasury said the companies and individuals provided support to armed factions in violation of an international arms embargo imposed on warring parties in the Congo conflict.

The measure is being coordinated with U.N. sanctions enacted this week against the individuals and companies, the department said in a statement.

The U.S. action includes sanctions against two Ugandan gold exporting firms, Uganda Commercial Impex and Macahnga Ltd, for what Washington says is their direct financial support to militias.

The department also put Straton Mussoni, a leader of a Rwandan militia, on its list of prohibited individuals for U.S. transactions.

Three other firms subjected to the sanctions were found to have ties to Viktor Bout, an international arms dealer who was sanctioned by the Treasury last October.

"These individuals and firms trafficked in plundered gold and arms at the cost of human lives," said Adam Szubin, director of the Treasury's Office of Foreign Assets Control. "We are taking action in concert with the U.N. Security Council to disrupt their activities and stem the violence in the Democratic Republic of the Congo."

Heavy fighting in Kinshasa erupted last week after troops loyal to former rebel leader Jean-Pierre Bemba defied an order to disarm and clashed with government troops.

European Union ambassadors said this week up to 600 people were killed in the two days of gun and mortar battles.

Last year, President Joseph Kabila defeated Bemba in the country's first democratic elections in over four decades, following years of corrupt leadership and a 1998-2003 civil war that left an estimated 4 million people dead.

After restoring order to the capital, Kabila has issued an arrest warrant for Bemba, the country's largest opposition group leader, who was waiting in the South African Embassy to travel to Portugal for medical treatment.

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