Iranian presidential candidate Mir Hossein Mousavi's call to his supporters to come dressed in black today when they gather in Tehran's streets appears to have been answered.

The Associated Press says "tens of thousands of black-clad" Mousavi supporters are again protesting the results of last Friday's election, in which President Mahmoud Ahmadinejad was declared the winner in a landslide.

The Guardian, which is again live-blogging, says it's been told by correspondent Saeed Kamali Dehghan that as many as one million people might be in the crowd.

And videos are starting to show up on YouTube of what is said to be scenes from today (NPR cannot verify the authenticity, so watch with that in mind):

Many more such clips are posted here.