In the continuing battle being fought over sanctions between the U.S. and Iran, Tehran warned the United States on Monday not to retake a seized supertanker released overnight. That tanker, allegedly carrying sanctioned crude oil headed toward Greece, was released by Gibraltar, which rejected an American appeal to detain the Iranian vessel longer.

In his first interview with an American network, a commander for the elite Iranian Revolutionary Guard claimed victory over the U.S. Commander Hossein Dehghan told CBS News the U.S. is behaving like "pirates" and called President Trump a "gangster."

But there's another battlefield in the sanctions war: a children's hospital. Since 1991, Mahek, a charity hospital in Tehran that offers free health care, has cared for nearly 30,000 children. But in the last year, vital drugs have been running out.

Iran produces much of its own pharmaceuticals. But when it comes to the most advanced medicines, it relies heavily on imports, and it's on imports that sanctions have had an impact.

Technically, medicines are exempt from U.S. sanctions, but the financial transactions to purchase them in the global marketplace are not. Imports have dropped by 80%, and the cost for the tiny amount of drugs that do make it in has skyrocketed.

For parents at Mahek who learn their child's cancer has come back, the agony is worsened when the cocktail of drugs needed to keep a child alive simply isn't available.

Four-year-old Mahdi's mother told correspondent Imtiaz Tyab that the most doctors can do now for her only child is keep him comfortable.

Four-year-old Mahdi's cancer has worsened. But sanctions have blocked the ability to acquire the drugs needed to save his life. CBS News

Dr. Shabnam Hemati, who heads the pharmaceuticals department, told Tyab that people are losing their lives because they cannot get drugs.

"What do you say to a parent whose child has cancer, that the drug is available outside Iran but not inside Iran?" asked Tyab.

"I tell them to pray and be sure that we are with you and we know your pain," she replied.

Doctors couldn't say how many children have died because of the inability to bring in medicine. But the charity's CEO told CBS News with 80% fewer drugs coming in you only have to do the math.