from datetime import datetime
import pytz


def _iso8601_to_localized_time(date_string):
    """
    Convert iso8601 date string into UTC time.

    :param date_string: iso8601 formatted date string.
    :return: :class:`datetime.datetime`
    """
    parsed_date = datetime.strptime(date_string, '%Y-%m-%dT%H:%M:%S.%fZ')
    localized_time = pytz.utc.localize(parsed_date)
    return localized_time