premise: Meanwhile, thousands of soldiers from the first Gulf War are still suffering from severe symptoms that have been linked to what is now known as Gulf War illness, say veterans advocates.
hypothesis: A least three soldiers are still suffering from severe symptoms that have been linked to what is now known as Gulf War illness.
reason: If thousands of soldiers from the first Gulf War are still suffering from severe symptoms that have been linked to what is now known as Gulf War illness, then it is definitely correct to say "A least three soldiers are still suffering from severe symptoms that have been linked to what is now known as Gulf War illness" because thousands is greater than three, so there are at least three.