Leader of Opposition in the Rajya Sabha Arun Jaitley said Afzal Guru's hanging had been delayed for reasons "the government has been unable to explain".
"Finally law took its own course. Public opinion compelled the government to act and enforce the law," Jaitley said.
Recalling the attack on Parliament House Dec 13, 2001, Jaitley said security officials and police personnel had sacrificed their lives to protect parliament and the people inside.
"India must today, as it did Dec 13, 2001, speak in one voice and give a clear message to the world that India is not a soft state and those who attack India, its sovereignty and its institutions, will be held accountable. Though belated, justice has been done," Jaitley said.
He said timely intervention of security personnel had foiled the attackers' plan to kill a large section of India's political leadership.
Referring to Afzal Guru's case, Jaitley said all judicial authorities had affirmed his guilt and upheld the death sentence. "His clemency petition had been rejected by the president," he said.
BJP leader M Venkaiah Naidu also asked why the government "inordinately delayed" Afzal Guru's execution, but welcomed his hanging.
"Perhaps the government is acting now against death convicts as it suffers from policy paralysis. Whatever the intention, the government has to explain the inordinate delay in the execution," Naidu told IANS.
Another BJP leader, Ravi Shankar Prasad added that the hanging "ought to have taken place much earlier. Why there was so much delay in taking this decision is a serious question".
Prasad attacked rights activists who did not want Afzal Guru to be hanged.
"What about the human rights of those killed in terror attacks? Those who lost their lives in protecting parliament? Are there no human rights for their families?" he asked.