The United Nations Human Rights Council is facing another key moment in its short history as it holds an emergency session on Sudan's Darfur region.
Non-governmental organisations fear deep splits within the 47-strong UN body will see the Sudanese government escape censure for ongoing violations.
The session started on Tuesday and continues on Wednesday after members failed to agree on what action to take.
Speaking at the opening, UN Secretary-General Kofi Annan called for an end to the "nightmare" in Darfur. The UN estimates that at least 200,000 people have been killed in the region since 2003 and more than two million others displaced.
"It is essential that this council send a clear and united message to warn all concerned... that the current situation is simply unacceptable and will not be allowed to continue," said Annan in a recorded message.
"The people in Darfur cannot afford to wait another day. The violence must stop. The killings and other gross violations of human rights must end."
It is the first time that the six-month-old council, which stems from a Swiss initiative, has devoted a special session to the humanitarian crisis.
Members finally voted to do so last month following heavy criticism from Annan, who accused the council of simply focusing on the Arab-Israeli conflict.
Skilful manoeuvring by Arab and Muslim countries ensured that all three previous special sessions were on the Middle East.
Member states are to debate two draft resolutions. One, submitted by Finland on behalf of the European Union, calls for an immediate end to "gross and systematic" violations and the dispatch of an independent mission to Darfur.
The other, put forward by Algeria on behalf of the African group, recommends that the council send its own team of officials and members.
Annan demanded on Tuesday that the human rights watchdog send a team of "independent and universally respected experts" to investigate abuses as soon as possible.
Addressing the session, Switzerland's ambassador to the UN in Geneva, Blaise Godet, described the situation in Darfur as "alarming and intolerable".
"Darfur is the scene of daily grave violations of human rights and humanitarian law. Civilians are the principal victims," he said.
Godet, who is vice-president of the council, said the Sudanese government had a duty to protect the population and to bring those responsible for crimes to justice.
He added that Switzerland supported the Finnish proposal and was ready to assist a mission of independent experts.
But NGOs, who have been demanding for some time that the Sudanese government be called to account, say they are far from confident that an acceptable compromise will be reached.
"It looks like we will end up with a weak resolution that will miss important elements like holding the Sudanese government accountable for human rights violations," Peter Splinter, Amnesty International's representative to the United Nations in Geneva, told swissinfo.
Geneva-based Human Rights Watch added that the special session would be a "farce" if it resulted in a weak resolution.
"We need a mission composed of experts for it to be credible," said spokeswoman Mariette Grange. "A mission made up of government representatives would inevitably have a political dimension."
UN Watch also fears the worst. Assistant executive director Elizabeth Cassidy told swissinfo that a fact-finding mission was likely to be the only positive outcome.
Last month the Human Rights Council rejected an attempt during its second regular session to hold the Sudanese government responsible for halting atrocities in Darfur, opting instead for a less-pointed resolution calling on all warring parties to end abuses.
The weaker resolution was the result of heavy lobbying by Khartoum, which invited ambassadors from African countries to Darfur days before the council resumed its recently completed third session.
swissinfo, Adam Beaumont with agencies
The Geneva-based council, which replaced the widely discredited Human Rights Commission, has so far focused most of its attention on the Arab-Israeli conflict.
The Darfur session is its fourth emergency session, following two special meetings on the Palestinian territories and one on Lebanon.
The UN Human Rights Council meets at least three times a year for a minimum of ten weeks and can call emergency sessions to respond to crises.
It is the most senior UN body based in Geneva.
Switzerland was elected to the council with a three-year mandate on May 9.
A country needs the support of at least 16 members to call a special session.