A bi-partisan group of U.S. congressional leaders was heading to the White House Wednesday to discuss a potential way to strike a ceasefire deal between Syria and Turkey, as Vice President Mike Pence heads overseas. But there was no sign that either side was about to stop its fight in northeast Syria. New video showed Turkish troops firing tank shells as they pushed harder in their battle against America's former allies in the region, the Kurdish militias who helped defeat ISIS. As CBS News correspondent Charlie D'Agata reports from inside Iraq, about 20 miles from that country's three-way border with Syria and Turkey, Pence may be headed to Ankara, but Turkish leader Recep Tayyip Erdogan has already said he "will never declare a ceasefire." Erdogan dismissed sanctions imposed on his government by President Trump earlier this week, and said the only option to end the Turkish offensive was for the Kurds to completely retreat from the land they've held for decades. Speaking Wednesday to Sky News, as Pence and Secretary of State Mike Pompeo were expected to fly to Ankara, Erdogan said he wouldn't meet with them, refusing to speak to anyone other than Mr. Trump himself. "I am standing tall. I will not meet with them," Erdogan told Sky. "They will meet with their counterparts. I will speak when Trump comes." Erdogan launched his offensive in Syria soon after a phone call with Mr. Trump last week. U.S. officials said Mr. Trump had been unable to convince Erdogan not to attack the Kurds, who had been vital American allies in the region for more than five years. One person Erdogan is talking to, however, is Russian President Vladimir Putin. The two leaders spoke over the phone Tuesday evening — the latest indicator of Russia's leading role on and off of the most complicated battlefield in the Middle East right now. As D'Agata reports, it's not just Syrian regime forces carving up Kurdish territory in northeast Syria; military vehicles flying Russian flags were seen driving around the flashpoint city of Manbij on Tuesday, and it's President Putin who now ultimately controls the area once dominated by U.S. forces and their Kurdish allies. Reporters from Russian TV channels were seen mocking America in a show-and-tell at the abandoned U.S. military base in Manbij on Tuesday. They showed off mess halls with half-eaten food, fully stocked refrigerators and personal items, suggesting the troops left in a hurry. CBS News has learned that American forces across northeast Syria have retreated to larger bases, like the one in Kobani, to begin airlifting heavy equipment out of the country. But it's a risky operation. When Turkish-backed militias - extremists made up of former al Qaeda and ISIS fighters - came too close to an American unit this week, the U.S. responded with a "show of force" in the form of Apache helicopters buzzing low to over the heads of the fighters to deter an advance. As the warzone widens, D'Agata said civilians escaping the violence are running out of places to go, with many crossing into neighboring Iraq to seek refuge. D'Agata said he saw himself refugees making a desperate break for the emergency exits. Before they had to make a run for the border themselves, he and his team visited multiple evacuated U.S. bases like the one in Manbij. In usual, well-planned withdrawals, most everything is packed away. But these bases looked like places frozen in time. CBS