Magnific Popup not closing when mfp-close button clicked

I have configured my popup as follows:

$('.xxx').magnificPopup({
      type:'iframe',
        closeOnContentClick: false, 
        closeOnBgClick: true,
        showCloseBtn: true,
        closeBtnInside: true,
        enableEscapeKey: true,
});

However, when pressing the '.mfp-close' button, the popup does not close. It only closes when I press the background or select the escape key. Finally, any attempt to capture the click event is ignored. How can I get this popup to close when hitting the button?