Senior Congress leader Shashi Tharoor has written to Lok Sabha Speaker Om Birla, alleging a "grave violation" of parliamentary privileges as well as a "blatant assault" on elected representatives and other peaceful protesters in his parliamentary constituency Thiruvananthapuram.

Kerala's capital Thiruvananthapuram witnessed incidents of violence on Saturday during protests organised by the Kerala Pradesh Congress Committee (KPCC) in which a battery of senior Congress leaders, including MPs and MLAs, suffered from suffocation and some were even hospitalised after police fired tear gas shells.

In a letter to Birla dated December 23, Tharoor said, "I am writing to you today to bring to your urgent attention a grave violation of parliamentary privileges as well as a blatant assault on elected representatives and other peaceful protesters that took place earlier today in my constituency of Thiruvananthapuram."

The incident took place at a rally where several fellow MPs, MLAs, leaders and several hundred workers from the Indian National Congress came together to register a peaceful protest condemning the recent spate of excesses by law enforcement agencies like Kerala Police against those critical of the current state government, which is seen widely as an attempt to "curb democratic dissent", he said.

"While the organisers of the rally had obtained the necessary permissions from various authorities to hold the protest, we were shocked when, without provocation or warning, tear gas shells were fired, landing just behind the stage while the Leader of the Opposition was addressing the rally.

"The subsequent fusillade of more tear gas shells were accompanied by water cannons, used by the police to break up the rally," Tharoor said.

"With skin, eyes and lungs still smarting, I have spoken in the strongest possible terms to the DGP, protesting this behaviour by his subordinates. He has promised a full enquiry," the MP said.

But the firing of tear gas shells against the stage, which was occupied by a number of senior public representatives, MPs and MLAs, clearly involves a serious breach of parliamentary privileges and immunities, he said.

"As the custodian of the House of which I am a member, I am writing to you today to urge you to look into this matter at your earliest convenience so that necessary action and strictures can be initiated in a time-bound manner," Tharoor said in his letter to Birla.

The manner in which elected representatives and hundreds of other victims were brutally assaulted by a completely unjustified and wanton attack by Kerala Police, using the highest-grade tear gas and water cannons against a peaceful protest rally, is a serious infringement on their basic democratic liberties and must be investigated immediately, he asserted.

"In light of these developments, I would be grateful if you could kindly examine the matter of the breach of Parliamentary privilege sympathetically and take appropriate action," Tharoor said.

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