LUCKNOW, India (Reuters) -A former lawmaker in India's parliament, convicted of kidnapping, was shot dead along with his brother while police were escorting them for a medical check-up in a slaying caught on live television on Saturday.

The dramatic footage of the men being killed was shared across broadcast channels and social media. A gunman is seen reaching over the shoulders of police to point a pistol at the temple of the former lawmaker, Atiq Ahmed, whose turban is blown off as the gun discharges.

His brother, Ashraf Ahmed, was shot a split second later.

In other footage, filmed by Reuters partner ANI, one gunman is seen firing repeatedly at brother's bodies as they lay on the ground.

The two victims died within minutes, while police quickly detained three men suspected of carrying out the slaying.

Media reports say the assailants had been posing as journalists. One surrendered immediately after the shooting, while officers subdued the other two suspects.

They had been among a throng of journalists that had gathered as the two brothers, allegedly kingpins in a local criminal organisation, were being brought, handcuffed from a hospital Prayagraj city in the northern state of Uttar Pradesh on Saturday evening.

After carrying out the slaying, the suspected gunmen shouted Hindu religious chants.

One policeman was wounded during the attack.

Fearing the possibility of violent unrest in the wake of the killings, the Uttar Pradesh government barred gatherings of more than four people across the entire state.

"The state government imposed restrictive orders after the killings of Atiq Ahmed and Ashraf Ahmed who were members of a large mafia involved in land grabbing and in murder cases," said a senior police official.

"We don't want any form of protest to gain momentum," the official said on conditions of anonymity as he is not authorised to speak with the press.

The state government, controlled by Prime Minister Narendra Modi's Hindu nationalist party, has ordered a judicial probe into the killings.

Last week police shot dead Atiq Ahmed's son in Jhansi city. He had been wanted in connection to a murder case that was being investigated as part of a wider crackdown into a land mafia operating in Uttar Pradesh.

Police in Uttar Pradesh have killed more than 180 suspected criminals during encounters over past six years.

The head of the opposition Samajwadi Party, said the slaying of his ex-party member while in police custody demonstrated the failure of the ruling Bharatiya Janata Party to bring law and order to Uttar Pradesh.

"When someone can be killed in firing openly amidst the security cordon of the police, then what about the safety of the general public," Samajwadi's Akhilesh Yadav said in a tweet.

Before losing an election in 2014, Ahmed had been a lawmaker with Samajwadi, and later the regional Apna Dal party.

(Additional reporting by Rupam Jain; Editing by Simon Cameron-Moore)