In its annual "World Report" filled with accounts of human rights violations around the world, the rights watchdog also applauded international efforts to bring peace to regions of Africa.
While charging world powers had not used enough "pressure" to end fighting in Syria, HRW reserved its strongest criticism for Russia and China.
"Despite a swiftly rising death toll and horrific abuses, Russia and China neutered the U.N. Security Council and enabled the killing of Syrian civilians by both sides," said Kenneth Roth, HRW's executive director.
The report claimed the two countries had "consistently protected" the Syrian government from U.N. action. It also charged the United States had been "reluctant" to pursue action against rights violators in the conflict to the International Criminal Court.
However, it praised actions by the African Union, France, the United States and the United Nations in aiding international missions to end the killing of civilians in conflicts in the Central African Republic and South Sudan.
The group also applauded advances "in the international machinery that helps to defend human rights." It noted increasing pressure by the U.N. Human Rights Council on North Korea and Sri Lanka. In addition, two treaties now protect domestic workers and miners poisoned by the unregulated use of mercury.
Referring to what it called "another major trend," HRW said purportedly democratic countries such as Egypt, Burma and Ukraine were paying "lip service to democracy" but cracking down on the rights of minorities.
The 667-page report also noted the "global outrage" related to government spying triggered by documents leaked by Edward Snowden, a former contractor for the National Security Agency.