Regular Lie groups and a theorem of Lie-Palais

In 1984 Milnor had shown how to deduce the Lie-Palais theorem on integration of infinitesimal actions of finite-dimensional Lie algebras on compact manifolds from general theory of regular Lie groups modelled on locally convex spaces. We show how, in the case of effective action, one can eliminate from Milnor's argument the abstract Lie-Cartan theorem, making the deduction rather elementary. A machinery employed in the proof provides a partial solution to a problem examined in 1972 by van Est and \'Swierczkowski.