<span style="color: #222222;">United States has warned that extremists may be plotting an attack against a major hotel in Nairobi and urged its citizens to be cautious. </span><br />'' <br />'' <span style="color: #222222;">US State Department urged US citizens to exercise increased vigilance if staying in hotels around Nairobi and to be aware of buildings' emergency evacuation plans.</span><br />'' <span style="color: #222222;"><br />'' Kenya has witnessed a series of bloody attacks carried out by al-Shabab, an extreme Islamist movement affiliated with Al-Qaeda that controls parts of neighbouring Somalia.<br />''<br />''In 2013, al-Shabab raid on Nairobi's upscale Westgate shopping mall left 67 dead in a siege that unfolded over four days.</span>