The US-based Human Rights Watch was among the signatories.
The press release also called on the summit to condemn human rights abuses by the Sudanese government, the Darfur rebels, and government-backed militias. It urged the Sudanese government to co-operate with the International Criminal Court's investigations into possible war crimes committed in Darfur.
Sudan contends that a UN presence is unnecessary, and that the 7,000-strong African Union (AU) force deployed in Darfur is capable of keeping the peace, provided it receives the necessary financial and logistical means to do so.
The issue of Darfur has featured prominently in the summit's discussions thus far. Sudan has attempted to garner the support of the Arab bloc to bolster its opposition to UN intervention in Darfur, but has had relatively little success.
Diplomats said that the initial draft resolution worked on by Sudan was deemed unacceptable by Amr Moussa, the Arab League's secretary-general, and a four-hour redraft offered only vague support for Sudan.
The draft resolution also does not commit the Arab states to financing the AU force, contrary to Khartoum's wishes.
However, the outcome of the summit seems likely to fall short of the NGO coalition's call for the Sudanese government to accept unconditionally the transition to a UN mission, as Khartoum has previously stated that it will not accept UN peacekeepers until a peace agreement is reached.
In addition, the draft resolution under discussion stipulates that Khartoum must approve any deployment of UN peacekeepers in its territory.
The press release also accused Khartoum of engaging in anti-UN propaganda by comparing the potential UN deployment with the American occupation of Iraq, a comparison described in the press release as "inflammatory misinformation".
It also noted that the Arab League's Commission of Inquiry to Darfur had condemned "massive violations of human rights" by pro-government militias, but that the commission's findings were subsequently played down after protests from Khartoum.
The NGOs also pointed out that the AU mission will require full funding and support in the months leading up to a possible UN deployment.