This report presents a short summary of detections within the international monitoring system (IMS) operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) after the nuclear accident at the nuclear power plant in Fukushima Daiichi, Japan on 11 March, 2011. The analysis presented in this report mainly covers measurements outside of Japan. Detections within the Swedish national network for particulate radioactivity in ground level air are also presented. The measurements indicate an initial eastbound spread of radioactivity from Fukushima, over the Pacific Ocean to North America and then passing the Atlantic Ocean to Europe and Asia. Later releases passed on a more southward route over the Pacific Ocean. About three weeks after the accident radioactive xenon was homogeneously spread over the northern hemisphere, and the activity concentration decreased with the rate of the physical half-life. The particulate radioactivity in the atmosphere decreased faster than the physical half-life of the radionuclides due to deposition. The particulate radioactivity from the accident was dominated by radioactive iodine. The results of the gaseous iodine measurements in Sweden indicate that the particulate fraction of the total iodine was only about 25 %. Apart from iodine, cesium and tellurium were also detected, however at lower activity concentrations. The activity reached Sweden about 10 days after the accident and measured radioactivity was dominated by 131I. Maximum concentration levels in Sweden were measured during 28 March - 2 April and the concentrations of 131I were below detection limits in the middle of May. In Sweden, measured radioactivity concentrations in air and deposition were only a fraction of measured activity levels after the Chernobyl accident in 1986. The accident at Fukushima will therefore not give any long term consequences in Sweden.