United Nations and Congolese troops have shelled rebels closing in on the city of Goma, in eastern Democratic Republic of Congo.<br /><br />They say the M-23 rebels are fighting on behalf of the Rwandan government.<br /><br />The rebels have captured strategic towns in the mineral rich North Kivu province over the past few weeks.<br /><br />Al Jazeera's Peter Greste reports from Goma.