US President Barack Obama on Monday extended for one year the existing sanctions on those involved in destabilizing Lebanon.

In a letter to Congressional leaders, the president said he was prolonging the freeze on assets, which was put in place by then President George W. Bush in August 2007 but set to expire on Thursday.

"Certain ongoing activities, such as continuing arms transfers to Hezbollah that include increasingly sophisticated weapons systems, serve to undermine Lebanese sovereignty, contribute to political and economic instability in Lebanon, and continue to constitute an unusual and extraordinary threat to the national security and foreign policy of the United States," he wrote.

"For this reason, the national emergency declared on August 1, 2007, and the measures adopted on that date to deal with that emergency, must continue in effect beyond August 1, 2013," Obama said, noting he was continuing the national emergency for one year.

The United States and Israel regard Hezbollah, a Shiite militant group and a major political force in Lebanon with close ties to Syria and Iran, as a terrorist organization. The European Union blacklisted the military wing of the group last week mainly over its involvement in the conflict in neighboring Syria.

In his executive order signed six years ago, Bush authorized a freeze on assets of anyone Washington deemed to be undermining Lebanon's pro-Western government.