In Kermanshah, where the largest demonstrations took place, protesters shouted slogans against the Iranian leader Ayatollah Khamenei.
Ayatollah Ali Khamenei said President Donald Trump has insulted the Iranian people ahead of an important national holiday.
"I have a Twitter account and I think it is a suitable tool for public diplomacy, connecting to people around the globe and voicing our ideas."
An exhibition of 150 submissions is now up in the Iranian capital, as Germany, Israel, UNESCO and others condemn the contest.
The remarks by Ayatollah Ali Khamenei followed a wave of arrests of journalists and intellectuals.
He had traveled from his home in Dubai to visit relatives.
Rouhani needs sanctions lifted quickly; Khamenei just ordered him to move slowly.
Khamenei said Iran would stop implementing the deal if the six powers imposed any new sanctions.
Bringing Russia in to bolster Assad's regime could risk Iran's strategic command of the situation in Syria.
The agreement has invigorated the Iranian president's foes rather than strengthen his position.
It's NOT a dating site, officials say.
Ayatollah Ali Khamenei has responded to overtures from U.S. President Barack Obama amid nuclear talks with a secret dispatch, The Wall Street Journal reported Friday.
The Twitter account, which is reportedly that of Khamenei,i has been using the hashtag #BlackLivesMatter
#FreeAmir campaign posts new video and heightens efforts to bring former U.S. Marine Amir Hekmati home as Iranian delegation arrives in New York