call a proc from c

hi all
soryy for multi posting, but:
is it possible to launch a tcl procedure (fire) containing tk command
from c.
here's a proc i would like to start:

proc fire {x} {
pack [label .l -text $x] -side top
}

when i try with Tcl_Eval, label is not recognize.
very very much thanks for any helps

.