US President Barack Obama decided on Thursday to extend for one year the national emergency over Libya, citing the need to guard against diversion of assets by members of the Gaddafi family.

In a letter to the Congress leaders, the president noted that Washington and its allies are in the process of winding down the sanctions against Libya in response to the "many positive developments" in the North African nation, including the fall of Muammar Gaddafi and his government.

"We are working closely with the new Libyan government and with the international community to effectively and appropriately ease restrictions on sanctioned entities, including by taking actions consistent with the UN Security Council's decision to lift sanctions against the Central Bank of Libya and two other entities on December 16, 2011," Obama wrote.

"However, the situation in Libya continues to pose an unusual and extraordinary threat to the national security and foreign policy of the United States and we need to protect against this threat and the diversion of assets or other abuse by certain members of Gaddafi's family and other former regime officials," he remarked.

"Therefore, I have determined that it is necessary to continue the national emergency with respect to Libya," he wrote.

Obama declared the national emergency over Libya on February 25, 2011, citing threats to US national security and foreign policy posed by Gaddafi and his government in their "extreme measures" against the people of Libya.

With the move, he ordered immediate sanctions on Gaddafi, his sons and Libyan government officials to counter what he called "a serious risk that Libyan state assets would be misappropriated by Gaddafi, members of his government, members of his family, or his close associates if those assets were not protected."

On March 19, Washington and its NATO allies began bombing Gaddafi's forces. The Libyan National Transitional Council officially announced the liberation of the country on October 23.