In the shocking footage, which comes after Spain sailed a warboat into Gibraltar waters, a Guarda Civil officer appears to point his weapon at what witnesses claim was an old man who had stepepd out of his car.
While it cannot be directly verified that the video was taken today, a friend of the cameraman told Express.co.uk he was sent the footage this afternoon on WhatsApp.
Spain has been forcing Gibraltarians to wait for hours in scorching heat at the frontier border after a war of words between Theresa May and the Spanish government erupted over the Rock's sovereignty in the aftermath of Brexit.
The policy delayed thousands of Spaniards who work on Gibraltar and were unable to get home.
A Spanish police officer brandished a gun at an old man at the Gibraltar border
Gibraltar's Chief Minister Fabian Picardo tweeted: "@GibraltarGov has been sent a video of an apparent firearms incident at the frontier. We are seeking details of the incident."
While Royal Gibraltar Police added: "@RGPolice is aware of a video on social media. It is filmed at the border and shows a Guardia Civil officer pointing a gun.
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"We cannot confirm that this occurred today. We are seeking clarification of the incident. Any witnesses contact Duty Officer on 20072500."
More to follow…