A rescue operation is underway to save an American caving instructor who fell ill a week ago while more than 3,400 feet deep in a cave in southern Turkey.

Mark Dickey, 40, fell ill on Aug. 31 while on an exploration of the Morca cave in the Taurus Mountains and has been unable to return to the surface since, according to the volunteer group New Jersey Initial Response Team.

Dickey is the chief of the group, which specializes in cave and mine rescue, as well as an instructor for the National Cave Rescue Commission.

The expert caver was helping lead an international caving expedition when he started suffering intestinal problems "that rapidly progressed into life-threatening bleeding and vomiting," the New Jersey Initial Response Team said in a statement.

"He was unable to get out under his own power and only the most experienced of cavers are capable of reaching him to render aid," the group said, noting that it takes experienced cavers about eight hours to reach where he is located in the deep, wet cave.

A medical team with the Hungarian Cave Rescue Service is assisting with the rescue mission, according to the European Speleological Federation. Doctors were able to reach Dickey on Tuesday and provide him with fresh fluids and blood to replace what he has lost and his condition appears to have slightly improved, though he is still unable to move on his own, the New Jersey Initial Response Team said.

Several other international rescue teams, including Croatian, Italian, Polish, Slovenian and American cave rescuers, "are waiting for the official invitation from the authorities," the European Speleological Federation said in a statement on Tuesday.

The Turkish military is also aiding in the remote rescue operation, according to the New Jersey Initial Response Team.

Rescuers are now preparing a camp at about 2,300 feet into the cave to which to move Dickey, and demolition teams are working to enlarge the narrow passages of the cave, the New Jersey Initial Response Team said.

Morca is one of the deepest caves in Turkey. Dickey is part of an expedition team hoping to collect samples from and map the cave beyond 3,400 feet, according to the team's website.

In 2014, more than 700 specialists rescued German spelunker Johann Westhauser, who was trapped for 12 days in one of Europe's deepest cave systems.