var str = '<div class="block"> <label>Country :</label> <option value="0">Select Country</option> <div id="input"></div>';

<div class="block">
<label>Country :</label>
<select onchange="with (this) if (selectedIndex) location = options [selectedIndex].value" class="selectpicker" data-style="btn-info" data-live-search="true">
<option value="0">Select Country</option>
<?php
include('db.php');
$sql = mysqli_query($con,"select * from user");
$userlink = "http://msgphp/users/";
$pphhpp = ".php";
$sle = "/";
while($row=mysqli_fetch_array($sql))
{
	$country_name = $row['user'];
	echo '<option value="'.$userlink, $country_name, $sle, $country_name, $pphhpp.'">'.$row['user'].'</option>';
}
?>
<script type="text/javascript">
	$(document).ready(function()
		{
			$(".country").change(function()
				{
					var country_id=$(this).val();
					var post_id = 'id='+ country_id;
					$.ajax
					({
						type: "POST",
						url: "ajax.php",
						data: post_id,
						cache: false,
						success: function(cities)
						{
							$(".city").html(cities);
						}
					});
				});
		});
	</script>
	</select>
	</div>