The region of South-East Europe has a long history of successful collaboration in sharing resources and managing distributed electronic infrastructures for the needs of research communities. The HPC resources like supercomputers and big clusters with low-latency interconnection are an especially valuable and scarce resource in the region. Building upon the successfully tested operational and policy models, the VI-SEEM project is focusing on establishing an integrated Virtual Research Environment that comprises not only HPC but also Grid, Cloud and Data management resources. By providing a common Authentication, Authorisation and Accounting system the VI-SEEM infrastructure simplifies the access to resources for research groups with complex workflows. Because of the diversity of hardware technologies, chosen by the different partners, the integrated infrastructure is able to fulfil widely different needs of HPC resources. Applications outside of the initial target user communities – Climatology, Life Sciences and Digital Cultural Heritage, are also accepted through open calls with a peer review process. Motivated by the challenges that the individual nations in the region are facing to provide HPC resources for their researchers, the integrated VI-SEEM infrastructure achieves optimisation of the use of the available resources and retention of the human capital of the region.