The Chinese mainland increased its holding of United States Treasury securities by $5.2 billion in May, retaining its position as the largest debtor of the US, preliminary data released on Tuesday by the US Department of the Treasury suggests.

At the end of May, the mainland held $1,169.6 billion, while it held $1,164.4 billion at the end of April, the data shows.

Japan remained the second largest debtor by holding $1,105.2 billion of US Treasury securities at the end of May.

China's Taiwan held $187.6 billion and Hong Kong held $145.4 billion, according to the data.