In a press freedom survey of 164 countries, Reporters Sans Frontieres ranked the United States 31st for its respect for freedom of expression at home, and 135th for its behaviour abroad.
Meanwhile, Israel ranked 44th and 146th in the two respective categories.
RSF said on Monday the US had caused the deaths of five journalists in Iraq. And it said the Israeli army was guilty of injuring and threatening journalists in the West Bank and Gaza.
RSF compiled the rankings by asking journalists, human rights activists, researchers and legal experts to complete a questionnaire evaluating press freedoms in their countries.
"The Israeli army's repeated abuse of journalists in the occupied territories and the US army's responsibility in the death of several reporters during the war in Iraq constitute unacceptable behaviour," the watchdog said in a statement.
Top ranked countries
The Paris-based organisation also complained about the arrest in Iraq on Sunday of a Reuters cameraman and an Agence France-Presse photographer who were covering the aftermath of an attack on a US convoy.
"Obstruction of journalists trying to do their job in Iraq is on the rise and must stop," RSF Secretary-General Robert Menard said. "The number of attacks on press freedom there is becoming alarming."
Twelve journalists were killed in the US-led Iraq war this year, and the US military was responsible for the deaths of five of them, an RSF spokesman said.
RSF also criticised Arab countries for cracking down on media freedoms during the Iraq war, but said standards were worst in Asia, with the region providing eight of the bottom 10 ranked countries.
"Concerned about maintaining their image and facing public opinion largely opposed to the war, they (Arab regimes) stepped up control of the press and increased pressure on journalists, who are forced to use self-censorship," RSF said.
Further east, Asia provided the biggest abusers of press freedom, as was the case in 2002.
Lowest ranked countries
1. North Korea
3. Burma (Myanmar)
The bottom 10 ranked countries included North Korea, rated the worst, Burma, Laos, China, Iran, Vietnam, Turkmenistan and Bhutan.
Cuba scored the second lowest after 26 journalists were arrested there earlier this year and sentenced to prison terms ranging from 14 to 27 years.
This made Cuba "the world's biggest prison for journalists", RSF said.
On the other hand, European Union countries generally scored highly, although Italy was placed 53rd - below most other EU states.