Fifteen Indian opposition MPs have been suspended after they protested against a security breach in the parliament.

At least four people were arrested after two intruders shouted slogans and set off coloured smoke inside parliament. Their motive remains unclear.

The federal home ministry has ordered an investigation into the incident.

The security lapse occurred on the 22nd anniversary of a deadly attack on the parliament.

On Thursday, a day after the breach, security was ramped up around the parliament building, with barricades outside the complex to restrict entry.

Both houses were adjourned after protests by opposition MPs who demanded a discussion on the incident and statements from the prime minister and the home minister.

In the Rajya Sabha, the upper house of the parliament, opposition MP Derek O'Brien was suspended for "ignoble conduct" after he shouted slogans demanding a statement from Home Minister Amit Shah.

In the Lok Sabha, the lower house, 14 MPs from opposition parties such as the Congress and the Dravida Munnetra Kazhagam were suspended until 22 December, when the session ends.

Before the session was adjourned, defence minister Rajnath Singh said in parliament that the incident had been condemned by "everyone". "We all - ruling and opposition MPs - have to be careful about to whom we issue the passes (to enter parliament)," he said.

Opposition leaders have demanded action against Pratap Simha, an MP from the governing Bharatiya Janata Party (BJP) who allegedly signed the passes used by the intruders to enter the public gallery in parliament.

Neither Mr Simha nor his party have officially commented. The BBC has emailed the MP for comment.

A police official told Reuters that visitor passes had been suspended until a security review was completed for the parliament building.

Reports say the four accused - three men and a woman in their 20s and 30s - will be produced in court on Thursday. Police have not officially confirmed their identities yet, but their families have been speaking to local media, and newspapers have published their photos and names.

The incident occurred on Wednesday while lawmakers were in session in the Lok Sabha, the lower house. Earlier in the day, President Droupadi Murmu, Prime Minister Narendra Modi and other leaders had paid tribute to the victims of the attack in 2001 in which nine people were killed. All five of the attackers were killed by the security forces.

MPs said two men jumped into the chamber from the public gallery and set off canisters of coloured smoke. One of the men was seen jumping from table to table as lawmakers and security officials tried to catch him.

Two others - a man and a woman - shouted slogans outside the parliament and set off coloured smoke from canisters. They were seen on video being led away by the police.

The four people who have been arrested are from different states in India - several media reports have quoted anonymous police officials who say they met on Facebook, but the BBC couldn't confirm this independently.

Some journalists outside parliament managed to speak to one of the accused as she was being led away by police. She identified herself as Neelam and said she did not belong to any organisation. She also said she was an ordinary citizen who was unemployed and wanted to protest against the government for clamping down on people.

Her family spoke to ANI news agency from their home in Jind district in the northern state of Haryana, and said that they did not know she had gone to Delhi. "All we knew was that she was in Hisar [in Haryana] for her studies," her brother said.

Neelam's family said she had several degrees, including a masters in education, but was concerned about unemployment.

"She used to tell me that she is so highly qualified but has no job, so it is better to die," her mother told ANI.

The man she was protesting with has been identified as Amol Shinde, from Latur district in Maharashtra state. A state minister told media that Mr Shinde had spent the last few years trying to pass police recruitment tests. Police say his family did not know his whereabouts.

The two men who entered parliament are Manoranjan D from Mysore in southern Karnataka state and Sagar Sharma from Lucknow in northern Uttar Pradesh state.

Manoranjan's father Devaraju Gowda told reporters that he condemned his son's act.

"This is wrong... You can protest outside [parliament] but not do this," he said, adding that Manoranjan had an engineering degree and would rear chicken, sheep and fish on the family's land.

"He reads a lot on Vivekananda [an intellectual and philosopher]. He only wanted to do good for society, for the deprived," Mr Gowda said. The family is from the constituency of Mr Simha, the lawmaker who allegedly signed the men in.

Sagar Sharma was the man who was filmed jumping on tables in parliament. His mother Rani Sharma said he was a tuk-tuk driver in Lucknow city.

"He had left two days ago," she told ANI. "He told me that he was going with his friends for some work."

Reports say a fifth man was detained in Gurugram on the outskirts of Delhi while another man was traced to Rajasthan. Both of them have been accused of helping the four protesters.

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