This report is taken from the following link and explains the activity of Hizb ut Tahrir in Yemen in its work for the Khilafah.http://www.presstv.ir/detail/194787.html
...Islamic group Hizb-Ut-Tahrir held a conference titled One Nation, One State and one Flag; calling all Yemeni's to join in the grindstone of establishing an Islamic State, which they say will unite all Muslims under the authority of Islam.
The Islamic conference was one of many this year addressed to a crowed of diverse supporters who view the establishment of an Islamic State as a divine order from God and an obligation which every Muslim should strive wholeheartedly for.
As the group has announced, they hope to uproot all current regimes separating the Muslim lands, and replace them with an Islamic government which they say will put into operation the laws of Islam rather than that of man-made laws.
(Read the rest at the link)