We study integral operators on $(-1,1)$ with kernels $k(x,t)$
which may have weak singularities in $(x,t)$ with $x\in N_1$,
$t\in N_2$, or $x=t$, where $N_1,N_2$ are sets of measure zero. It
is shown that such operators map weighted $\fL^\infty$--spaces
into certain weighted spaces of smooth functions, where the degree of
smoothness is as higher as smoother the kernel $k(x,t)$ as a function in $x$.
The spaces of smooth function are generalizations of the
Ditzian-Totik spaces which are defined in terms of the errors of best weighted
uniform approximation by algebraic polynomials.
Keywords:
Weakly singular integral operators,
Weighted spaces of continuous functions, Approximation spaces