A number of incursions have taken place around Gibraltar's waters in recent years (Picture: MOD).
The Defence Secretary was "speaking in jest" when he suggested the British military uses paintballs against ships trespassing in Gibraltar's waters.
It is thought Gavin Williamson made the proposal in a meeting with defence chiefs before Christmas.
In response, the Ministry of Defence said: "While the Defence Secretary was speaking in jest about paintballing Spanish ships, he is in favour of the Royal Navy taking a strong stand against Spanish incursions into sovereign British waters."
There have been numerous instances of Spanish ships crossing into Gibraltarian waters in recent years, with the Royal Navy being deployed to chase out vessels carrying out incursions.