By Karolina Tagaris ATHENS (Reuters) - Greek Prime Minister Alexis Tsipras welcomed on Friday proposals to create a European Union coast guard agency to patrol its vast sea borders as pressure built at home for a solution to growing numbers of migrants stranded in the country. The proposal was initially put forward by France and Germany out of frustration that Greece's inability to stem an influx of hundreds of thousands of refugees across the Aegean sea was threatening the EU's open-border Schengen zone. Under a European Commission plan, the proposed coast guard could be deployed without a request from the state in question, unlike Frontex, the EU border agency already deployed in Greece, which needs an invitation.