Syrian President Bashar al Assad on Wednesday blamed U.S. sanctions and pressure on the United Nations and Syria’s neighbors for the reticence of more than 5 million refugees who fled the conflict there to return.

“There are many hurdles,” Assad said, citing U.S. sanctions at the opening of a conference in Damascus, co-hosted by Moscow.

Of Syria’s 17 million people, 5.5 million are living as refugees in the region, mostly in Turkey, and a further six million are uprooted within their own country.

Assad said millions of refugees were being forced to stay in host countries by “pressure or intimidation” and that host states were enticing them financially while benefiting from international aid for them.