Federal agents and detectives from the Madison police department are investigating a claim by a pro-choice group that it was behind a weekend arson attack on an anti-abortion office in Wisconsin.

The headquarters of Wisconsin Family Action in Madison was attacked in the early hours of Sunday, with a molotov cocktail thrown through a window, starting a small fire, and graffiti spray-painted on an exterior wall. Nobody was hurt.

In a statement reported on Tuesday by the Lincoln Journal Star, which said it was unable to verify the group’s authenticity, Jane’s Revenge said it launched the attack because of the organization’s anti-abortion stance, and demanded that similar institutions across the US disband or face “increasingly extreme tactics”.

“Wisconsin is the first flashpoint, but we are all over the US, and we will issue no further warnings,” the statement said, citing the violence of anti-choice groups who “bomb [abortion] clinics and assassinate doctors with impunity” as justification.

The Madison attack came days after the leaking of a supreme court draft ruling that would overturn its 1973 Roe v Wade decision and end almost half a century of constitutional abortion protections.

On Tuesday, a spokesperson for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) told the Guardian that its agents were aware of the group’s claims of responsibility, but cited the ongoing investigation for being unable to give more details.

The Madison police department said it was “aware of a group claiming responsibility for the arson at Wisconsin Family Action and are working with our federal partners to determine the veracity of that claim”.

It urged anyone with relevant information to make contact, saying: “We take all information and tips related to this case seriously and are working to vet each and every one.”

At a press conference on Monday afternoon, the Madison PD and ATF agents announced a joint investigation into what it called an “abortion extremism case involving an arson and graffiti attack of a pro-life advocacy office in Madison”.

The Madison police chief, Shon Barnes, said no suspects had so far been identified. Authorities were expected to give a further update on Tuesday afternoon.

In a values statement on its website, Wisconsin Family Action (WFA) describes itself as a Judeo-Christian group dedicated to “strengthening, preserving, and promoting marriage, family, life and liberty.

“We support the sanctity of human life from the moment of conception through natural death. This includes opposing legislation that promotes the destruction of human life – which starts at conception – through abortion and other means,” it says.

Jack Hoogendyk, the WFA board chairman, attacked the response to the attack in a tweet posted on Tuesday morning, singling out Wisconsin’s Democratic governor, Tony Evers, and Madison PD detectives.

“We need to see a much stronger message of condemnation of this activity from our Governor [and] from local law enforcement,” he wrote.

At a press conference on Monday, Evers called the attack “a horrible incident”.

Calling for a full investigation and arrests, he added: “As the state of Wisconsin, we don’t accept that type of violence here.”

An attack on an anti-abortion office is a relative rarity compared with attacks on abortion clinics and providers. In 2019, the Guardian reported on an “alarming escalation” in picketing, vandalism and trespassing by anti-abortion activists at medical facilities.

Arson, bombings, murders and acid attacks were among more than 300 acts of extreme violence recorded by the Rand Corporation between 1973 and 2003, and in one of the most heinous incidents, in 2009, Dr George Tiller, a Kansas abortion provider, was shot dead in a church in Wichita.

In March, MS magazine reported that the number of brick-and-mortar abortion clinics nationwide had dropped precipitously, partly because of the constant threat of violence against personnel. Six states, MS said, had only one abortion provider, mostly small, independent operators who were considered most at risk.

“Abortion clinics have been closing at an alarming rate,” the article said. “Independent providers are the most vulnerable to anti-abortion attacks and violence directed at their staff.”