Call to undefined function xml_parser_create_ns()

I have installed davical on Ubuntu 16.04. I can connect with a client to the server, but the http-requests fails. I have started a request from cli and got following response:

curl --request PROPFIND --user ds:xxx --header "Content-Type: text/xml" --header "Brief:t" --data "<D:propfind xmlns:D="DAV:"><D:prop><D:displayname/></D:prop></D:propfind>" http://localhost/davical/caldav.php/ds/addresses/
Exception [0] Call to undefined function xml_parser_create_ns()
At line 562 of /usr/share/davical/inc/CalDAVRequest.php
================= Stack Trace ===================
/usr/share/davical/htdocs/caldav.php[76] CalDAVRequest->__construct()

I think, the problem is "Call to undefined function xml_parser_create_ns()". How can I fix it?

Php version is 7 and davical 1.1.4.