Jason Russell was recovering in hospital suffering from malnutrition and exhaustion, Invisible Children's chief executive said. Photograph: Brendan Mcdermid/Reuters


One of the co-founders of Invisible Children, the San Diego-based charity which is campaigning for the arrest of Ugandan warlord Joseph Kony, has been hospitalised after police said he was arrested for being naked and masturbating in public.

Jason Russell, 33, was picked up by police in San Diego at around 11.30am on Thursday after receiving numerous calls from the public about a man vandalising cars, being apparently under the influence of a substance and making sexual gestures while wearing only his underwear.

According to local TV station NBC, San Diego police spokeswoman Lieutenant Andra Brown told a press conference in the city that Russell was co-operative as he was detained by officers. "He was no problem for the police department. However, during the evaluation we learned that we probably needed to take care of him. So officers detained him and transferred him to a local medical facility for further evaluation and treatment," she said.

Invisible Children has shot to fame in recent weeks after one of the videos that it produces in order to publicise the atrocities of Kony and his Lord's Resistance Army went viral. Viewed more than 76m times, the video gave a high profile to the group's cause, but also put the tiny charity at the centre of global scrutiny.

Critics have condemned the group for a perceived lack of transparency in its financial records and for over-simplifying a complex issue. They accused the group of being fame-seeking and of having an overtly western focus on what is a regional African problem. Some also pointed out the group had taken large donations from rightwing Christian fundamentalists groups in the US, who have also funded anti gay-rights causes.

However, the group and its many defenders mounted a strong defence, detailing its financial history and saying that their sole aim was to highlight a dreadful and ongoing human rights cause that had garnered little attention for decades. They were also hailed for using social media to engage young people in social activism.

Scores of support groups have sprung up all over the US and the world and a resolution of support for the groups' aims has even been introduced in Congress. The group is planning a day of mass action in protest at Kony for next month that aims to distribute more than a million posters bearing the logo Kony 2012 across the US.

A brief statement by the group in the wake of Russell's arrest said that being at the centre of a massive media storm may have taken its toll. "Jason Russell was unfortunately hospitalised suffering from exhaustion, dehydration and malnutrition. He is now receiving medical care and is focused on getting better," said Invisible Children's chief executive Ben Keesey in the statement.

"The past two weeks have taken a severe emotional toll on all of us and that toll manifested itself in an unfortunate incident yesterday. Jason's passion and bis work have done so much to help so many and we are are devastated to see him dealing with this personal health issue."