gdb-ia hangs

I have a fortran program that compiles fine with

ifort -r8 -g prog.f90 -mkl

and also executes fine with a.out, but when I do

gdb-ia a.out

followed by

(gdb) start

or

(gdb) starti

it says something like  

Starting program: ...............

[New Thread 0x1703 of process 20050]

end then just hangs without giving a further (gdb) prompt.

Am I doing something wrong?

Thanks, Boris