Siberian investigators are seeking jail terms over a prank in which a billboard for a clinic treating sexually transmitted diseases was doctored to include less-than-flattering portraits of Dmitry Medvedev and Vladimir Putin.

The original billboard for the Barnaul clinic depicted gonorrhea, candida and ureaplasma as ugly monsters under the slogan: "Do you need such companions?"

The pranksters added a row of personified disease photos, including a ghastly white President Medvedev, a light green Prime Minister Putin and similarly ill-looking likenesses of Communist leader Gennady Zyuganov, Liberal Democratic Party leader Vladimir Zhirinovsky and Altai Governor Alexander Karlin, according to photos posted on the local anarchist web site Anarhobarnaul.org.

The ad also carries the address of another web site for radical leftist activism, Avtonom.org.

Local investigators said Thursday that the three suspects are "members of the radical Antifa organization." The incident occurred in February but is still being investigated, it said in an online statement.

Searches at the suspects' residences have yielded masks, baseball bats, unspecified leaflets and "extremist literature," it said.

Two suspects, Sergei Sandin and Daniil Malyshkin, both members of the Barnaul Anarchist Movement, were detained a day after the billboard appeared, while a third, Vitaly Leonov, was exposed two weeks later, Novaya Gazeta reported in March.

In the searches, investigators simply seized all books with the words "anarchy," "fascism," "anti-fascism," "revolution" and the like, Leonov told Novaya Gazeta.

None of the trio has been kept in custody, but all three may end up in prison for up to seven years if charged and convicted of hooliganism, investigators said.

Putin and Medvedev have typically avoided comment on their likenesses being parodied. Both have been targets of street campaigns before, including this summer, when an anonymous graffiti artist identified only as Monolog.tv put up spoof billboards for the Hollywood movie "Captain America: The First Avenger" that presented Medvedev as "Captain Russia" across Moscow. No prosecution followed.