Strange sky phenomenon photographed over Piriápolis in Uruguay

Witness wonders if the phenomenon in the sky over Piriápolis in Uruguay is caused due to an effect of city lights or a UFO. 

The green shade and ring-shaped object were not visible at the time he shot the two photographs. 

If we compare the first and second picture, it seems as the ring-shaped object has moved over the city. 

Mufon case 63402.