We report an early result from the ICARUS experiment on the search for a ν μ →ν e signal due to the LSND anomaly. The search was performed with the ICARUS T600 detector located at the Gran Sasso Laboratory, receiving CNGS neutrinos from CERN at an average energy of about 20 GeV, after a flight path of ∼730 km. The LSND anomaly would manifest as an excess of ν e events, characterized by a fast energy oscillation averaging approximately to (sin^{2}(1.27Delta m^{2}_{mathrm{new}}L/E_{ u})approx 1/2) with probability (P_{ u_{mu} ightarrow u_{e}} = 1/2 sin^{2}(2 heta_{mathrm{new}})). The present analysis is based on 1091 neutrino events, which are about 50 % of the ICARUS data collected in 2010–2011. Two clear ν e events have been found, compared with the expectation of 3.7±0.6 events from conventional sources. Within the range of our observations, this result is compatible with the absence of a LSND anomaly. At 90 % and 99 % confidence levels the limits of 3.4 and 7.3 events corresponding to oscillation probabilities (langle P_{ u_{mu} ightarrow u_{e}} angle le 5.4 imes 10^{-3}) and (langle P_{ u_{mu} ightarrow u_{e}} angle le 1.1 imes 10^{-2} ) are set respectively. The result strongly limits the window of open options for the LSND anomaly to a narrow region around (Δm 2,sin2(2θ))new=(0.5 eV2,0.005), where there is an overall agreement (90 % CL) between the present ICARUS limit, the published limits of KARMEN and the published positive signals of LSND and MiniBooNE Collaborations.