There is described, in accordance with a first aspect of the invention, a laser treatment system and method for, in particular, imparting beneficial residual stresses into a desired part (P) during production thereof by a Selective Laser Sintering or Melting (SLS/SLM) process, the method including the step of repeatedly subjecting the desired part (P) to an in-situ Laser Shock Peening (LSP) treatment as the desired part (P) is gradually being produced during the SLS/SLM process. The in-situ LSP treatment includes selectively bringing an LSP module (20) in contact with a surface (S) of the desired part (P) being produced during the SLS/SLM process and subjecting the LSP module (20) to the action of a first laser beam (LLSP) to impart beneficial residual stresses into the desired part (P). According to this first aspect of the invention, the LSP module (20) is movable between a building chamber (30) where the desired part (P) is being produced, for the purpose of carrying out the in-situ LSP treatment, and a separate storage chamber (35) located adjacent to the building chamber (30), when the LSP module (20) is not used for the purpose of carrying out the in-situ LSP treatment. This first aspect of the invention is implementable in a corresponding additive manufacturing system and method. Further aspects of the invention are described.