The Chilean air force has located debris believed to be from a cargo plane that crashed this week with 38 people aboard over a remote stretch of frigid sea between South America and Antarctica.

The debris, which was found 18 miles (30km) south of where the plane last made contact, will be recovered for analysis to determine if it belonged to the Hercules C-130 cargo plane, the air force said in a statement.

The aircraft disappeared shortly after taking off late on Monday from the southern city of Punta Arenas. The air force concluded the aircraft must have crashed early the next morning, given the number of hours it had been missing.

“We will continue the search and hope for a better result,” Gen Eduardo Mosqueira, who leads the search effort, told reporters.

The cause of the crash was unknown and officials acknowledged the slim chances of finding survivors.

Earlier on Wednesday, the Chilean military sent fighter jets in an expansion of its search after large rolling waves in the icy Drake Passage and low clouds had complicated the mission the day before.

Mosqueira said the search area covered an area of about 250 by 280 mile (400 by 450km). He told reporters that improved visibility was helping the crews of searchers using planes, satellites and vessels from Argentina, Brazil, Uruguay and the US as well as Chile.

The flight appeared routine until the moment it disappeared, Mosqueira said.

The region where the plane disappeared is a vast, largely untouched ocean wilderness of penguin-inhabited ice sheets off the edge of the South American continent with depths of 11,500ft (3,500 meters).

The military was using sonar-enabled navy ships to detect irregularities at depth, and that it had established quadrangles to help organize the search, Mosqueira said. Ships from Argentina and Brazil were assisting, he said.