Efforts to help millions of people in need in Sudan due to the civil war are being hampered by a lack of security and meagre international funding, the United Nations said Thursday.

The army, led by Abdel Fattah al-Burhan, has been battling the paramilitary Rapid Support Forces commanded by his former deputy Mohamed Hamdan Daglo, after the two fell out in a power struggle.

"We need to reach 18 million people and we will not give up on that target," Clementine Nkweta-Salami, the UN's resident and humanitarian coordinator in Sudan, told reporters.

"But we need more international support, better access to the people who need us and safety for our operations."

She highlighted that 19 members of humanitarian organisations have been killed and 29 others injured since the conflict erupted.

While she did not comment on whether they had been specifically targeted, she noted that "in many instances, our efforts are being hampered", despite indicating "where it is we will be, and what we will be doing".

The fighting in Sudan broke out on April 15.

"The past six months has caused untold suffering in Sudan," Nkweta-Salami said.

- Aid in the crosshairs -

Nearly 7,500 people have been killed in Sudan since the conflict began, according to a conservative estimate from the Armed Conflict Location & Event Data project.

Fighting has displaced almost 4.3 million people within Sudan, while around 1.2 million more have fled across its borders, UN figures show.

Among them, "we've seen a significant brain drain. A lot of the professionals have left Sudan", said Nkweta-Salami.

Humanitarian aid has become a target for attacks and looting by armed gangs and criminals.

"We have been able to deliver assistance through a cross-border mechanism from Chad and into Darfur," Nkweta-Salami said.

"In mid-September, nearly 3,000 metric tonnes of aid supplies were delivered by 66 trucks across six states. But we need to be able to deliver much more -- safely, repeatedly, and fast."

The UN has relocated its headquarters to Port Sudan on the Red Sea as the fighting in the capital Khartoum made the international organisation's work impossible.

The obligatory presence of soldiers while loading trucks in Port Sudan and delays in obtaining visas are all additional obstacles in getting aid around the country.

- $2.6 billion needed -

One of the poorest countries in the world, Sudan has seen its health system brought to its knees by the conflict, with 70 percent of hospitals no longer functioning, said Nkweta-Salami.

The UN official said she was worried that heavy rains and floods could lead to more outbreaks of water-borne diseases.

"Battling a cholera outbreak in a war zone is difficult at the best of times. With fighting escalating, it may be near-impossible to control," she said.

Despite the complex humanitarian crisis, the UN is battling a funding shortage.

"The $2.6-billion humanitarian appeal is just one-third funded," said Nkweta-Salami.

"The population of Sudan is balancing on a knife edge as their country is gradually consumed by this conflict," she said.

"There's also a risk that... if this situation is not brought to an end, that it will have a spillover effect in the region and that is something we must and should avoid."