Stonehenge monuments that have stood for thousands of years appear unscathed after climate protesters were arrested for spraying orange paint on them, an official said Thursday.

Workers cleaned the stones and the roughly 4,500-year-old monument was visibly undamaged, said Nick Merriman, the chief executive of English Heritage.

鈥淚t鈥檚 difficult to understand and we鈥檙e deeply saddened,鈥� Merriman told BBC Radio 4. 鈥淚t鈥檚 vandalism to one of the world鈥檚 most celebrated ancient monuments.鈥�

The UNESCO World Heritage Site site reopened and was expected to host thousands of revelers celebrating the summer solstice, the longest day of the year in the Northern Hemisphere, early Friday.

Stonehenge was built on a windswept plain in southern England in stages starting 5,000 years ago. Its origin and purpose remain somewhat of a mystery though the stone circle aligns with the summer solstice sunrise and winter solstice sunset, drawing crowds of spiritualists, druids and sun worshippers.

A 73-year-old man and 21-year-old woman were released on bail Thursday after being arrested a day earlier on suspicion of criminal damage, damaging an ancient monument and deterring a person from engaging in a lawful activity.

The climate change activism group Just Stop Oil took responsibility for the act Wednesday and released video showing a man it identified as Rajan Naidu blast a fog of orange from a fire extinguisher at one of the vertical stones.

People gathered at the site could be heard yelling 鈥渟top鈥� and one person intervened, running up to Naidu and grabbing his arm. As the person struggled to pull him away from the monument, another man joined the tussle and and wrestled the paint can free.

The second protester, identified as Niamh Lynch, 21, managed to spray three stones before she was stopped.

Just Stop Oil said the paint was made of cornstarch and would dissolve in the rain.

Merriman said experts cleaned the orange powder from the stones because they were concerned about how it might react to water.

The publicity stunt was among a long line of disruptive acts by Just Stop Oil to draw attention to the climate crisis. The protests have halted sporting events, sullied famous works of art and caused traffic jams. The acts have led to convictions, jail terms and widespread criticism.

The Stonehenge demonstration was swiftly condemned by Prime Minister Rishi Sunak, who called it a 鈥渄isgraceful act of vandalism.鈥� His main opponent in the election next month, Labour leader Keir Starmer, called the group 鈥減athetic鈥� and said the damage was 鈥渙utrageous.鈥�

The group struck again Friday when it took credit for spray painting private jets at an airport outside London. Two women were arrested.

Brian Melley, The Associated Press