Xbee modules are an option, as are other 800 to 900 Mhz RF modules, but subject to some constraints.
I suggest you make your choice by looking at Digi's comparison matrix table of the different Xbee options; there are at least three that suit your application, and they are point-to-multipoint capable.
The table states you can get outdoor range up to 40 km (for example, with the XBee-PRO 868), but note a couple of things:
this is outdoors range; if the same transmission were attempted in an indoors environment (or generally a situation where there are intererence sources within the Fresnel zone), your range will drop markedly.
this requires using a high-gain antenna, so that may be a constraint depending on what your device construction allows (in fact, I think most of the distances specified in that table are with a dipole antenna).
some of the model variants are only available selectively in Europe or North America, if this matters.
for some insight on performance metrics, it's worth reading this app note, where they demonstrate nearly 0% packet loss at distances up to 40 km range, but with specific conditions.
Note that the data rate for the long-range models might not meet your requirement of 100 Kbps, which is a tough ask although...
Alternately, GSM modules perform your bandwidth requirement easily in a different context, which brings up an alternate idea: You can also consider instead using GSM modules for your communication, although this obviously might turn pricey since you state there are on the order of a 100 users.
One final suggestion is to use the low- or medium-range Xbee models, but use extenders/repeaters/relay-units to cover the required distance (or in case of the Zigbee variant of Xbee, you can even use the units in the mesh as extenders themselves). Setting up a robust Zigbee network takes some development effort, but this is somewhat simplified with the firmware stack on the Xbee ZB units.