The international community should stop signing deals with firms that provide arms to Syrian President Bashar al-Assad's regime amid an uprising that has left thousands dead, Human Rights Watch said Sunday.

The New York-based rights group singled out Rosoboronexport, Russia's state-owned arms trading company, in an open letter to the firm and a statement published on Sunday.

"The bottom line is that no one should do new business with any company that may be an accomplice to crimes against humanity," Kenneth Roth, HRW's executive director, said in the statement.

He added: "Rosoboronexport's clients should distance themselves from the company until it stops selling arms to Syria."

HRW said in the statement that under international law, "providing weapons to Syria while crimes against humanity are being committed may translate into assisting in the commission of those crimes."

"Any arms supplier could bear potential criminal liability as an accessory to those crimes and could face prosecution."

More than 13,400 people have been killed across Syria since an anti-regime uprising erupted in March 2011, including nearly 2,300 since a ceasefire technically went into effect on April 12, according to figures compiled by the Syrian Observatory for Human Rights.