New York, May 14 (IANS): The Pakistan government should investigate and bring to justice those responsible for the attack on members of the Ismaili Shia community in Karachi that killed 43 people, Human Rights Watch said on Thursday.

An extremist group called Jundullah, a splinter group of the Tehreek-e-Taliban (TTP), or Pakistani Taliban, claimed responsibility for the attack in which six gunmen opened fire on a bus carrying Ismaili Shia to a community center.

The attack highlights the vulnerabilities of Pakistan's Shia and other religious minorities to attack, Human Rights Watch said.

The Karachi attack indicates that despite the government's tough rhetoric against armed groups since the December 2014 TPP attack on a school in Peshawar that left 148 dead, they remain a potent threat to religious minorities.

"The carnage in Karachi suggests that Shia and other religious minorities are at risk anywhere in Pakistan," said Phelim Kine of Human Rights Watch.

"Anyone who believed that the government measures put in place after the December attack in Peshawar would resolve the problem of extremist violence needs to think again."

Extremist groups such as the TTP and Lakshar-e-Jhangvi (LeJ), a Pakistani Taliban-affiliated organisation, view Shia Muslims as heretics whose killing is therefore justified.

The LeJ have targeted in particular the Shia Hazara minority in Balochistan's provincial capital of Quetta, causing hundreds of deaths since 2008.

"The Karachi attack is a bloody indictment of the government's lack of political will to tackle the sources of violence against the Shia and other religious minorities," Kine said.

"Until the government arrests and prosecutes the leaders of groups responsible for such atrocities, religious minorities will remain at serious risk."