The dictionary meaning of to claim is "to demand as one's own, to assert and demand the recognition of a right". "In the U.S.A. loosely", adds the dictionary, "it is used in the sense of to assert or to allege".
This "loose" usage is no longer confined to the U.S.A. Here are some recent examples from this country:
The police took statements from about forty people who claimed that they had seen the gunmen in different parts of the city.
The State Department claims that discrimination is being shown against the American Film Industry.
There are those who claim that the Atlantic Treaty has an aggressive purpose.
I have a friend who claims to keep in his office a filing tray labelled "Too Difficult."
This use has become so common, and is found in such respectable places, that the fight against it should probably be regarded as lost. That will be deplored by all those who like to treat words as tools of precision, and to keep their edges sharp. Why should claim, which has its own useful job to do, claim a job that is already being efficiently done by others? Perhaps the idea underlying this usage is that the writer claims credence for an improbable assertion.