McCain torpedos Republican effort to repeal Obamacare

US Senator John McCain has announced his opposition to the latest Republican attempt to replace Barack Obama's signature health care law, likely dooming the repeal effort.

"I cannot in good conscience vote for the Graham-Cassidy proposal," Mr McCain said of the bill proposed by fellow Republican senators Lindsey Graham and Bill Cassidy.

"I believe we could do better working together, Republicans and Democrats, and have not yet really tried," the senator said in a statement.

In July, Mr McCain made a dramatic return to Washington from Arizona after a brain cancer diagnosis to become one of three Republican senators who helped sink their party's earlier efforts to replace Obamacare.

Republicans have pledged to repeal Obama's health care reforms, but have struggled to secure enough support to do so amid fears that proposed alternatives would dramatically increase the number of Americans without health insurance.