NEW DELHI: Four planes, including one bound for the United States, received bomb-threat messages through a social media handle on Tuesday, prompting security agencies to undertake specific counter-terrorist drills at various airports, official sources said.

The threats via microblogging platform X came a day after three international flights originating from Mumbai received bomb threats, causing trouble to hundreds of passengers and airline crew. The messages posted on Monday were declared hoax.

The sources said an X handle issued threats on Tuesday to four planes -- an Air India Express aircraft from Jaipur to Bengaluru via Ayodhya (IX765), a SpiceJet plane from Darbhanga to Mumbai (SG116), an Akasa Air plane from Siliguri to Bengaluru (QP 1373) and an Air India plane from Delhi to Chicago (AI 127).

Precautionary measures are being taken in all the cases, aviation security sources told PTI.

The X handle tagged the airline and police handles, claiming that bombs were placed on these planes, the sources said.

Four different X handles had issued a similar threat to three international flights originating from Mumbai on Monday.

All the messages on Monday were declared hoax after security and intelligence agencies as well as airlines and airport operators carried out stipulated anti-terrorist security drills that are activated in case of bomb or hijack threats, the sources said.

Officials said the Bureau of Civil Aviation Security (BCAS) has sought the help of Indian cyber-security agencies and police to trace the person or people behind these threats.