Two Ukrainian fighter jets were shot down Wednesday over separatist-held territory not far from the site of the Malaysia Airlines crash as international outrage over the tragedy has done little to slow the fierce fighting in eastern Ukraine.

While Kiev made significant advances against rebels in the country's east in recent days, Ukrainian and U.S. officials say Russian weapons are continuing to pour over the border. The escalation in fighting suggests Russian President Vladimir Putin has no intention of dialing back his support...