For signatories to the 1967 Outer Space Treaty*, yes. For everyone else, no.
Note that a Daedalus-style propulsion system would not be banned under the terms of the treaty because it is not a weapon (although you could reasonably expect international observers to attend testing and launches.)
http://www.ucsusa.org/global_security/space_weapons/page.cfm?pageID=1157
* The Outer Space Treaty is actuall incorrectly named: it should be called the Inner Space Treaty, as Outer Space refers to everything outside the Solar System.