UML2 sequence diagrams are interaction diagrams which have been used largely to model the behaviour of objects interaction in systems. These diagrams suffer from lack of precise semantics due to the semi-formal nature of the UML notation. This problem hinders the automatic analysis and verification of such diagrams. Process algebras have been used largely in order to deal with such problem. In this paper, we propose a mapping of CombinedFragments of UML2 sequence diagrams into π-calculus specifications and use the Mobility Workbench (MWB) tool for the verification of these diagrams. The mapping provides a formal semantics as well as formal analysis and checking for UML2 sequence diagrams. We illustrate our approach by an example to prove the usefulness of the translation.