"The government of Iran must allow human rights groups to monitor and report facts from the ground on the ongoing protests by the Iranian people. There can not be another massacre of peaceful protesters, nor an internet shutdown. The world is watching," Efe news quoted Trump as saying in a tweet.
Protests in Iran erupted in November 2019 following a rise in oil prices, which have eventually turned into demonstrations against the Islamic Republic's theocratic regime, while leaving at least 304 dead and thousands injured in the violence and crackdown, according to Amnesty International.
The Iranian government blocked the Internet for six days to check the organization of these protests.
In an earlier tweet published in both English and Persian, Trump expressed support for Saturday's protests in Tehran, where hundreds of Iran raised slogans against the government and the Islamic Revolutionary Guard Corps (IRGC).
"To the brave, long-suffering people of Iran: I've stood with you since the beginning of my Presidency, and my administration will continue to stand with you. We are following your protests closely, and are inspired by your courage," said Trump.
The protests came on the same day the IRGC admitted that one of its missiles had downed the Kiev-bound Ukraine International Airlines (UIA) flight PS75, killing all 176 people on board, mistaking it for a possible "US cruise missile".
Meanwhile, the UK's Ambassador to Tehran, Rob Macaire, was arrested while protesting against the Iranian government in the capital city and detained for more than an hour, the British Foreign Ministry said on Saturday, while criticizing the incident as a violation of international law.
"The arrest of our Ambassador in Tehran without grounds or explanation is a flagrant violation of international law," said Foreign Secretary Dominic Raab.
"The Iranian government is at a crossroads moment. It can continue its march towards pariah status with all the political and economic isolation that entails, or take steps to deescalate tensions and engage in a diplomatic path forwards," he added.
The UK's Sky News reported that Macaire was arrested on suspicions of organizing, provoking and directing the so-called radical actions.
( With inputs from IANS )