"We are… especially concerned about the citizens from our own country currently under detention abroad: individuals such as Roxana Saberi in Iran, and Euna Lee and Laura Ling in North Korea," Obama said in a statement marking World Press Freedom Day on May 3.
He also said he was using the occasion to "sound the alarm about the growing number of journalists silenced by death or jail as they attempt to bring daily news to the public."
US-Iranian reporter Saberi, who marked her 32nd birthday in jail Sunday, was sentenced to eight years in prison on charges of spying for the United States, allegations Washington says are unfounded.
Her father, Reza Saberi, told AFP in Tehran that his daughter was now into her second week on a hunger strike, in which she takes only sugared water, and that despite losing lots of weight would keep up her protest until she is released.
Euna Lee, a Korean-American, and Laura Ling, a Chinese-American, were detained by North Korea March 17 along the Tumen River which marks the border with China.
Pyongyang said Friday the two female journalists would stand trial on criminal charges, a move seen by some analysts as pressuring Washington to open direct dialogue.
The North had previously said the pair would face trial for "hostile acts" and illegally entering the country.
Obama decried the jailing or active harassment of journalists that have taken place "in every corner of the globe," including China, Cuba, Eritrea, Myanmar, Sri Lanka, Uzbekistan and Zimbabwe.
"Emblematic examples of this distressing reality are figures like J.S. Tissainayagam in Sri Lanka, or Shi Tao and Hu Jia in China," he said.
Obama noted that since World Press Freedom Day was first celebrated in 1993, 692 journalists have been killed as they worked "to expose truth and enhance accountability around the world."
