At least 10 armed men disguised as policemen have attacked a high-security prison in India's Punjab state, injuring jail guards and freeing a top commander of a Sikh armed group and four others, officials said.

The attackers travelled in cars and stormed Nabha Jail on Sunday, stabbing a guard at the main gate and firing rounds of live ammunition before fleeing with the inmates, who included the Khalistan Liberation Force (KLF) chief Harminder Singh.

KLF is an armed group fighting for a separate Sikh homeland in Punjab.

Singh, who is also known as Mintoo, was arrested in 2014 and is on trial for "terror attacks and funding".

READ MORE: 1984 anti-Sikh riots - Calls for justice in India

The four others who were freed are part of a local criminal gang and were on trial for murder.

Unconfirmed local media reports said the attackers numbered around 20.

"We have sounded an alert in the state and formed special teams to nab them," HS Dhillon, Punjab director general of police for law and order, told AFP news agency.

A senior police officer said the assault took guards by surprise as the attackers moved quickly through the complex, indicating they knew the jail layout.

Punjab's deputy chief minister said state police were "investigating conspiracy between terrorists and gangsters to disturb peace in Punjab before elections".

Prison officials sacked

Four officials, including the Punjab prison chief and jail superintendent, have either been suspended or sacked following the jailbreak, authorities said.

A reward of $36,000 has been offered for information on the escaped prisoners.

Punjab was in the grip of an armed conflict for almost three decades since the 1970s after several Sikh groups launched an armed campaign for an independent Sikh country.

The violence peaked following the 1984 storming of Amritsar's Golden Temple - holiest shrine in Sikhism - by the Indian army to flush out armed fighters.

The military operation angered Sikhs, resulting in the assassination of Indian Prime Minister Indira Gandhi by her Sikh guards and thousands of Sikhs taking up arms to avenge the sacrilege.

More than 20,000 people, mostly civilians, died during the unrest of late 1990s in Punjab.

But several Sikh groups remain committed to the Khalistan movement and dozens of alleged fighters remain imprisoned.

Last month, eight men awaiting trial escaped a prison in Madhya Pradesh state before shot dead hours later in a shoot-out, which many allege was staged by police. 

Sikhs still seek justice on riot anniversary

Source: News Agencies