Mortar Fired From Roosevelt Island - Fact Or Fiction From Soderbergh's Che Movie?

Image of Benicio del Torro as Che from LA Times

The Crooks and Liars blog reviewed the soon to be released Steven Soderbergh movie Che. Of particular interest to Roosevelt Islanders was this brief portion of the review.

... The recreations of Che’s visit to New York in 1964 and speaking at the United Nations seem so real as to be actual documentary footage. But again, it is not. Soderbergh shoots in front of the U.N. and in either the actual General Assembly chambers or an amazing look-alike set.

Touched on in a brief film recreation are a bomb attempt of the U.N. (which I knew about) and the firing of a mortar across the East River from Roosevelt Island it seems (which I didn’t know about)...

I have never heard of a mortar firing from Roosevelt Island either and was wondering if this was true or just a fictionalized scene from the movie. After all, Southpoint Park is closed to the public when the UN General Assembly is in session. Potentially scary stuff.

Mortar image from Steven Soderbergh.net