An Indian army patrol, comprising one Non-Commissioned Officer and five other ranks, was "ambushed on our side" of the LoC in Poonch sector of Jammu and Kashmir, he said in identical statements in the Lok Sabha and the Rajya Sabha.
"The ambush was carried out by approximately 20 heavily-armed terrorists along with persons dressed in Pakistan army uniform," he said.
"In the ensuing firefight, five Indian soldiers were martryred and one soldier was injured," he said.
Strongly condemning the "unprovoked incident", Antony said, "I assure the House that our army is fully ready to take all necessary steps to uphold the sanctity of LoC."
He said the Government of India has lodged a strong protest with the Pakistan government through diplomatic channels.
His statement came after members expressed anger over the incident and wanted to know how the government was responding to it.