Narendra Modi addresses during an election rally. File
The nuclear-armed neighbours have fought three wars, and last February came close to a fourth with tit-for-tat airstrikes sparked by an attack on Indian troops in Kashmir.
Modi is under pressure after weeks of protests against a new citizenship law, a slowing economy and the prospect of losing the latest in a string of state elections in New Delhi next month.
"Pakistan has already lost three wars. Our armed forces will not take more than 7-10 days to make Pakistan bite the dust," Modi said in a speech to military personnel.
Pakistan swiftly rejected the "belligerent rhetoric," calling Modi's comments "irresponsible and war-mongering."
A statement from the foreign office said it reflected India's "incurable obsession" with Pakistan."
Wearing a maroon National Cadet Corps baseball cap at the event in the capital, Modi said India's new prowess was thanks to what he called "youthful thinking."
He said that Indian strikes against what New Delhi said were militants in Pakistan-administered Kashmir and inside Pakistan proper in 2016 and last year were evidence of this.
"This is 'youthful thinking'. We carry out surgical strikes and take on terrorists in their homes," Modi said.
Last year, however, an Indian fighter jet was shot down and the pilot captured by Pakistan after a rare aerial engagement.
The premier's message came as the curfew and communications blackout imposed by New Delhi in Kashmir entered its 12th day. Aug.15 is also India's Independence Day, which is being observed as a black day across Pakistan to protest the brutalities in Kashmir.
As per a statement issued by the Prime Minister Office, the decision has been "taken in view of the regional security environment.” Bajwa's tenure was due to end in November but analysts have long predicted the extension.
"The people of Pakistan also desire peaceful, cooperative relations with all neighbours, including India," Imran Khan said in his reply, adding, "I thank you for your letter conveying greetings on Pakistan Day."
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