UNITED NATIONS - The United States has asked for targeted UN sanctions to be imposed on Yemen's former president Ali Abdullah Saleh and two Houthi rebel leaders for threatening the peace and stability of Yemen and obstructing the political process.Washington submitted a formal request on Friday for the United Nations Security Council Yemen sanctions committee to subject the men to a global travel ban and asset freeze. The committee is due to discuss the request on Tuesday, diplomats said.Yemen, a US ally with a population of 25 million neighboring oil-producing giant Saudi Arabia, is trying to end political unrest that began with mass protests against Saleh, president for 33 years until he stepped down in 2012."As of fall 2012 Ali Abdullah Saleh had reportedly become one of the primary supporters of the Huthi rebellion. Saleh was behind the attempts to cause chaos throughout Yemen," the United States said in its 'statement of case' obtained by Reuters."More recently, as of September 2014, Saleh is reportedly inciting instability in Yemen by using the Huthi dissident group to not only delegitimize the central government, but also create enough instability to stage a coup," it said.