CPI(M) general secretary Sitaram Yechury made the remarks after the government briefed the Opposition on the standoff and also on the Kashmir issue.
Yechury, however, asked the government to reflect and introspect why "suddenly" India's neighbourly ties in the region have "deteriorated".
The Marxist leader sought to know why the intelligence inputs available before the attack on Amarnath pilgrims "was not used" and how the bus carrying pilgrims was allowed to go off on its own, as he demanded accountability for the "lapse" be enforced immediately.
"The government briefed us on the stand-off with China and said that efforts are on to resolve this through diplomatic channels and talks.
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"We fully support the government in these efforts. We are for peace and tranquillity with all our neighbours. This is in India's supreme interest," he said in the post.
Yechury reiterated the opposition's position that the situation in Jammu and Kashmir has "worsened" in the past three years and asked the government to correct its "faulty" approach.
"The government must answer," he stressed.
The Rajya Sabha member also said that the "growing" instances of lynchings and attacks on minorities and Dalits are also adding to the view that the deteriorating internal security environment in the country is a "matter of grave concern".