There’s no native way to do this — and I’ll spare you the lecture about editing delivery formats, because, let’s face it, you’re reading this because you’re probably stuck with one.
You can stuff around with AviSynth scripts, or you can give up and transcode using Handbrake or another 3rd party tool — or you can be clever about it and use a remuxing tool that’s much faster and better quality. SmartLabs have a freeware (not open source) product called tsMuxeR (edit: link reported broken in comments — mirror)that will do exactly this that worked like a charm on Windows 7, but there are also versions for Linux and OS X available.
Worth a shot if you’re stuck with a video file Premiere doesn’t want to know about.

I’m using Premiere CS3 and I have an Matroska MKV file that I need to import. I downloaded and ran tsMuxeR, as you suggested, but none of the output files will open in Premiere. Can you tell me what I’m doing wrong? Which options did you use in tsMuxeR? Thanks so much for your help.
- Johnny
Try Pavtube Video Converter, did the trick for me. Cheap and fast.
Thanks! Works great. Here’s a working link to the tool, the one in the post is broken.
http://www.videohelp.com/tools/tsMuxeR
JohnnyW, m2ts is supported in CS5, not sure about for CS3.
:) thanks!
Oh man, this worked like a charm. Thank you so much!
I’m using Premiere CS5 and I have an Matroska MKV file that I need to import. how can i do this?