Iran ? A Russian-made jetliner carrying 168 people nose-dived into a field after taking off from the Iranian capital on Wednesday in a fiery crash that shredded the aircraft and killed everyone aboard — Iran’s worst air disaster in six years. Witnesses say the plane’s tail was on fire before it went down.

It was the latest in a string of deadly crashes in recent years that have highlighted Iran’s difficulties in maintaining its aging fleet of planes.

Iranian airlines, including state-run ones, are chronically strapped for cash, and maintenance has suffered, experts say. U.S. sanctions prevent Iran from updating its 30-year-old American aircraft and make it difficult to get European spare parts or planes as well. The country has come to rely on Russian aircraft, many of them Soviet-era planes that are harder to get parts for since the Soviet Union’s fall.