'End in sight' in campaign to retake Raqqa from ISIS, says top diplomat

— -- It began on the 73rd anniversary of D-Day -- the U.S.-led Allied invasion of Normandy, France during World War II -- and now, less than four months later in ISIS's self-declared capital, "the end is now in sight," according to a top U.S. diplomat.

The fight for Raqqa, Syria, has been bloody and prolonged, but Brett McGurk, the special presidential envoy to the Global Coalition to Defeat ISIS, said Friday that the terror group is down to its last three neighborhoods in the north-central part of the city.

"It is a matter of time until the operation in Raqqa is finished," McGurk added.

There are still a host of ISIS fighters holed up in the city, but the U.S. has shot down speculation that they may be promised safe passage out of the city -- as they were in a deal with Lebanese terror group Hezbollah. That deal was vehemently opposed by Iraq and the U.S., leading to a standoff where American forces picked ISIS fighters off as they tried to escape.

A State Department official told ABC News they are not aware of any such arrangement or discussions and, "I can't predict every situation, but it is pretty hard to imagine such a scenario given previous comments by [Defense Secretary James] Mattis that we are not going to let them get out."

Enormous challenges remain even after Raqqa falls, though -- illustrated, McGurk said, by one statistic Secretary of State Rex Tillerson shared with the Global Coalition this morning. Tillerson chaired a summit Friday of the group and its top diplomats on the sidelines of the United Nations General Assembly in New York. At one water treatment facility outside the city, Tillerson told the assembled members, teams found 240 un-exploded ordinances left by ISIS -- a "salt the earth tactic ... when they know they're going to lose," McGurk said.

To address that, the State Department and its sister organization USAID have a small team of development experts in Syria -- now on their third month there -- who assist in "stabilization" efforts to restore basic necessities -- de-mining, water treatment, rubble removal, aid logistics, restoring electricity and more.

Raqqa's fall is crucial to disrupting the terror group's network, especially their ability to plan and coordinate attacks abroad, according to McGurk. The city was where ISIS launched attacks on Istanbul, Paris and Brussels.

ISIS was planning "major, significant terrorist attacks, the type of Sept. 11-type events that they aspire to" from the city, McGurk said. That capability, in at least this one ISIS stronghold, is now gone.

After Raqqa, the coalition will turn its attention to Deir al Zour and smaller outposts in the Euphrates River Valley in eastern Syria. There, the Syrian Democratic Forces and their U.S. backers have faced a delicate dance with the Assad regime, its Iranian militia allies and its Russian backers as they also make a play to disrupt ISIS from the city. The bulk of ISIS's foreign fighters and its leadership are believed to be holed up there.