  Monopole operators in Abelian N=4 Chern-Simons theories described by circular
quiver diagrams are investigated. The magnetic charges of non-diagonal U(1)
gauge symmetries form the SU(p)xSU(q) root lattice where p and q are numbers of
untwisted and twisted hypermultiplets, respectively. For monopole operators
corresponding to the root vectors, we propose a correspondence between the
monopole operators and states of a wrapped M2-brane in the dual geometry.
