Indian police say they took a pigeon into custody after it was found with a note threatening the prime minister.
The bird was found near the border with Pakistan.
"We took it into custody last evening," Pathankot police inspector Rakesh Kumar told AFP by telephone on Monday.
"The BSF [Border Security Force] found it with a note in Urdu saying something like: 'Modi, we're not the same people from 1971. Now each and every child is ready to fight against India.'"
Prime Minister Narendra Modi was elected in 2014 and since then has increased spending on India's defence.
A ceasefire agreed in 2003 remains in place, but neighbouring India and Pakistan often accuse each other of violating it.
Officers say the bird was discovered at Pathankot in the northern state of Punjab, where Pakistan-based militants launched a deadly attack on an airforce base in January.
The two nations have been rivals for a long time, with the last full war between India and Pakistan taking place in 1971.
The note was apparently signed by the Pakistan-based militant group Lashkar-e-Taiba (LeT) "so we are investigating the matter very seriously", Kumar said.
Two balloons were also recently found in Punjab with similar messages addressed to Prime Minister Narendra Modi in Urdu.
Last year, another pigeon was arrested by police in India on suspicion of being a spy from Pakistan.
In 2013, Indian security forces found a dead falcon fitted with a small camera and in 2010 another pigeon was detained over spying fears.
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