Single line, frequency tunable lasing was observed in an optically pumped, repetitively pulsed, room temperature CO laser for the first time. The R(0) and R(7) ro-vibrational transitions in the (2,0) overtone of CO at 2.3 micrometer were optically pumped with a high-energy optical parametric oscillator (OPO). Single line lasing was observed on (2,1) P(2)-P(17) transitions and R(0)-R(11) transitions (covering wavelengths within the range 4.6 - 4.9 micrometer) when using a diffraction grating as the spectrally selective reflector of the laser resonator. The observed CO laser pulse lengths were approximately 10-7 seconds with peak power being up to 104 W. The influence of CO pressure, addition of buffer gas (He, Ar), Q-factor of the laser resonator, and pump pulse energy on CO laser pulse temporal characteristics and output energy spectral distribution was studied experimentally.