(CNN) -- Hours after supreme leader Ali Khamenei warned fellow Iranians against continued protests of last week's official election results, plans for further demonstrations appeared to move forward Friday as signs of tightened security emerged.
Khamenei's blunt warning against the continuation of such protests, which he delivered during Friday's morning prayers, was ignored by hundreds if not thousands of Iranians. Their voices of defiance rose Friday night from their rooftops in Tehran, where they shouted "Death to the dictator" and "Allah akbar," or "God is great," according to sources and video posted on YouTube.
The tactic is a reprise of one that swept across the city in 1979, when the Islamic revolution led by Ayatollah Ruhollah Khomeini toppled the shah.
A source in Tehran whose descriptions of events there have proved credible during the recent unrest told CNN in an e-mail that on Friday night, he drove through a road checkpoint set up by the Basij militia, a volunteer paramilitary force that takes orders from the government.
"Older and younger Basijis, holding huge guns, were checking out passing cars for potential 'trouble-makers,' " he wrote, describing the situation on the street as "quasi martial law." Watch a report on Khamenei's warning »
Witnesses have said Basij militia members have attempted to impose order by beating demonstrators during the week of protests that followed the government's pronouncement that President Mahmoud Ahmadinejad had won last week's election by a landslide.
On his Facebook page, opposition leader Mir Hossein Moussavi, who has called for a new vote, said he would publish a list of locations for demonstrators to gather in the coming days. He urged his readers to spread the information to others.
Meanwhile, the source said, pro-Moussavi Iranians were waiting to hear whether a rally being planned for Saturday would be held.