New Delhi | As the West Asia crisis reaches a critical flashpoint following Washington's ultimatum to Tehran, India on Tuesday advised its nationals in Iran to stay wherever they are for the next 48 hours.

In an urgent advisory, the Indian embassy in Iran urged Indians to remain indoors and strictly avoid military installations, power infrastructure and the upper floors of multi-story buildings.

US President Donald Trump warned that a "whole civilisation will die tonight" if Iran does not meet his 8 pm Eastern Time deadline (5:30 am Indian time, Wednesday) to end its blockade of the Strait of Hormuz.

"In continuation of previous advisories, Indian nationals who are still in Iran must stay where they are for the next 48 hours, avoiding all electric, military installations and upper floors of multi-storey buildings, remaining indoors and coordinating any highway movement strictly with the embassy," the mission said.

"Those in embassy-hired hotels should stay put indoors while maintaining regular contact with on-site embassy teams. All are requested to monitor official updates closely," it said.

The embassy said its emergency numbers remain operational.

According to official data, around 9,000 Indians, including students, were in Iran when the conflict began following strikes on Iranian targets by Israel and the US on February 28. Nearly 1,800 Indians have returned to India so far.