UN High Commissioner for Human Rights Navi Pillay has raised concern about threats to the rule of law in Papua New Guinea, which has been locked in a leadership battle.
The nation's politics have been in turmoil since August 2011, when parliament elected Peter O'Neill as prime minister while then-leader Sir Michael Somare was recovering from illness in Singapore.
Somare contests the legitimacy of the vote - a view upheld by the Supreme Court, which ruled in December that O'Neill's rise to power was illegal.
Pillay accused O'Neill's government and parliament of interfering with judicial independence with a new law on judicial conduct.
"One after another, the executive and parliament have taken very worrying steps to interfere with judicial independence," she said in a statement.
"It appears that the Judicial Conduct Act is being used to interfere in particular with the legal proceedings to determine the legality of the current administration," she added.
"The judiciary must be allowed to operate free from external pressures, threats or executive or legislative interference - international law is clear on this matter."
Pillay also raised alarm over reports that several journalists had been attacked, and called for "prompt investigations".
"Papua New Guinea is on a slippery path to upending the constitutional order and undermining the rule of law," she said.
PNG has a June constitutional deadline to hold elections, but O'Neill has shrugged off pressure to hold them on time - notably from Australia, the impoverished country's major aid donor.
Somare, who has dominated politics in the country for decades, believes he is still the leader of the nation of 6.6 million people, and fresh elections are viewed as a way of resolving the dispute for good.