At least 192 people have been killed in two weeks of protests against the government and economic strain in Iran, a rights group said on Sunday, in a sharp rise from an earlier death toll of 51.

Iranians took to the streets in new protests against the clerical authorities overnight despite an internet shutdown, as rights groups warned on Sunday that authorities were committing a "massacre" to quell the demonstrations.

Major Iranian cities were gripped overnight by new mass rallies denouncing the Islamic republic, as the son of the ousted shah urged protesters on Saturday to plan to seize city centers.

Venezuela was set to hold talks on Saturday with U.S. envoys in Caracas on restoring diplomatic ties, days after U.S. forces deposed Nicolas Maduro as its president.

South Africa on Saturday began naval drills with Russia, Iran and China, describing the manoeuvres off its coast as not merely a show of force but a vital response to rising maritime tensions.

Iran's supreme leader Ayatollah Ali Khamenei on Friday insisted that the Islamic republic would "not back down" in the face of protesters who he called "vandals" and "saboteurs", in a speech broadcast on state TV.

Speaking to supporters in his first comments on the escalating protests since January 3, Khamenei said U.S. President Donald Trump's hands "are stained with the blood of more than a thousand Iranians" and predicted the "arrogant" U.S. leader would be "overthrown" like the imperial dynasty that ruled Iran up to the 1979 revolution.

Russia on Friday said the United States had decided to release two Russian members of the crew of a Russian-flagged oil tanker that Washington seized earlier this week.

"In response to our request, U.S. President Donald Trump has decided to release two Russian citizens aboard the Marinera tanker, previously detained by the United States during an operation in the North Atlantic," Russian foreign ministry spokeswoman Maria Zakharova said in a statement.

U.S. President Donald Trump said on Friday he cancelled a second wave of attacks on Venezuela after it began releasing "large numbers" of political prisoners this week.

"Venezuela is releasing large numbers of political prisoners as a sign of "Seeking Peace."... Because of this cooperation, I have cancelled the previously expected second Wave of Attacks," he said on his Truth platform.

Iranian protesters shouted and marched through the streets into Friday morning after a call by the country's exiled crown prince for demonstrations, despite Iran's theocracy cutting off the nation from the internet and international telephone calls.

Short online videos shared by activists purported to show protesters chanting against Iran's government around bonfires as debris littered the streets in the capital, Tehran, and other areas. Iranian state media broke its silence Friday over the protests, alleging "terrorist agents" of the U.S. and Israel set fires and sparked violence. It also said there were "casualties," without elaborating.

Russia said Friday it has used the new Oreshnik ballistic missile along with other weapons in a massive strike on Ukraine.

Ukrainian officials said four people were killed and at least 22 wounded in the capital overnight. Russia didn't say where Oreshnik hit, but Russian media and military bloggers said it targeted a huge underground natural gas storage facility in Ukraine's western Lviv region.