After China blocked action at the United Nations against Pakistan for freeing 26/11 mastermind Zaki-ur-Rahman Lakhvi, Prime Minister Narendra Modi expressed India's grave concern "at the highest levels" to Beijing, said sources.
Sources said PM Modi raised India's concerns regarding China's stand on Lakhvi with senior Chinese leader and Standing Committee chairman of the National People's Congress, Zhang Dejiang, who was in Delhi last week.
Lakhvi, accused by India of planning and executing the terror attacks in Mumbai in which 166 people were killed, was released in April from a Pakistani prison.
The UN Sanctions Committee, which met earlier this month in New York at India's request, was to seek a clarification from Pakistan on Lakhvi's release; however, China blocked the move on grounds that India did not provide sufficient information.
The move came a month after China put "on hold" India's efforts to place Syed Salahuddin, the chief of Pakistan-based terror group Hizbul Mujahideen, on UN terror list.
Lakhvi, 55, was arrested in December 2008; he was a top commander of the terror group Lashkar-e-Taiba. Lakhvi is on trial, along with six others, for the worst-ever terror attacks in India, but the case has made no progress in five years in Pakistan, creating a major stress point in bilateral relations.
India's permanent representative to the UN, Asoke Mukherjee, wrote to the UN's Sanctions' Committee terming Lakhvi's release a violation of a UN resolution on terrorist organisations and groups, including the al Qaeda and the Lashkar-e-Taiba (LeT), wherever located.
The sanctions committee includes China as a permanent member of the UN Security Council.