"ark" - not "arch".
If it still exists, it's present location is unknown.
It is not inside any mosque. It was "lost" hundreds of years before Muslims existed - even before the Babylonian Captivity, which occurred roughly 1,200 years before Muslims existed.
Two very reputable rabbis claim to have seen it in a cave beneath the temple mount in the 1940s - but they were unable to reach it from where they saw it. It is true that the temple mount is riddled with caves, and it is true that no exploration of those caves has been permitted since, I believe, the early 1950s. It is not unreasonable that, in a cave system, they could see something that they could not physically reach (quite common in cave systems, in fact). However, no one has ever verified their claim.
The Ethiopian Orthodox Church claims to be in possession of it, and claims that they have been in possession of the true ark since the time of Solomon (at which time, their legend goes, the "Ethiopian" son of Solomon by the Queen of Sheba replaced the true ark in the temple with a fake and brought the true ark back to Ethiopia). This legend, IF I remember correctly, first appeared in the 13th century C.E. (I may be wrong about the date) during a civil war in Ethiopia between two brothers. The brother who claimed to possess the ark of the covenant had people flock to his side and he won the war. If you search the internet, you can see a photo of an Ethiopian priest wearing a "hat" that is a representation of the Ethiopian ark - an object they still possess, whether or not it is the true ark.
the ark of the covenant should contain
* the stone tablets on which are written the ten commandments
* Aaron's rod
* a gold "coffer" or "covered pot" in which manna has been preserved
Jim, http://www.bible-reviews.com