Three babies who died during childbirth are among the civilian deaths West Papuan leaders are blaming on a brutal crackdown by Indonesian forces in the region of Nduga.

They are calling for Indonesia to allow humanitarian and medical agencies access to the area, as well as foreign media.

Since West Papuan guerrillas launched a deadly attack on a Nduga construction site in early December, Indonesia has conducted heavily armed operations in and around the jungle in a bid to track them down.

The United Liberation Movement for West Papua (ULMWP) claims thousands of civilians have been displaced, 10 people have been shot by Indonesian military (TNI) – six of them killed – and several people have been detained and allegedly tortured.

“About four women gave birth in the bush and three children died,” Benny Wenda, the exiled leader of the ULMWP, told Guardian Australia. “Some are missing. There are more numbers on people coming but we know for the moment around 11 people are dead and some places we can’t access.”

The ULMWP, which is the umbrella organisation for West Papuan independence organisations, said: “Without urgent action by international humanitarian, aid and human rights organisations, more Papuan civilians will be at risk.

“International observers and the West Papua people are lobbying for urgent access to West Papua to provide immediate medical treatment, food aid, medical support, documentation and resources to villagers; and to investigate the illegal use of chemical weapons.”

Indonesia was accused of using the internationally banned white phosphorus chemical weapon against civilians, a charge it denied. It also denied TNI has targeted civilians, and said it had provided protection for them to return to their homes.

Q&A Why is there unrest in West Papua? Show The Indonesian provinces of Papua and West Papua share an island with Papua New Guinea, and its indigenous population has been engaged with a low-level insurgency with Indonesia for about half a century. After the departure of Dutch colonisers, and disagreement between Papuans, the Netherlands, and Indonesia, the United Nations sponsored a treaty appointing Indonesia as temporary administrator. In 1969 a UN resolution affirmed the so-called “Act of Free Choice”– a referendum which saw 1,026 hand-picked West Papuans vote to remain with Indonesia, but which has been repeatedly dismissed by international observers as unrepresentative and coerced. Indonesia maintains the regions have always been Indonesian and the resolution simply affirmed its sovereignty. A guerrilla separatist movement grew and violence has continued ever since, with claims more than half a million West Papuan people have been killed, as well as countless arrested and injured, and villages destroyed. Indonesia is regularly accused of human rights abuses, which it denies. In recent years the West Papua cause has gained increased support from regional neighbours, including Vanuatu, Tuvalu, and the Marshall Islands, but a 2017 independence petition – signed by 1.8 million West Papuans and smuggled out of the country to the UN’s decolonisation committee – was rebuffed as outside its mandate.

Wenda said the ULMWP believed at least 11 people were dead as a result of the TNI crackdown, and a number of people were missing or in hiding.

“They are scared to come out because Indonesia is bombing through helicopters. People are really scared,” Wenda said. “This is like my childhood in 1977, with the bombs on my village, and a lot of people missing and scared to come home.”

The Indonesian military operation was sent in after at least 17 people were killed on 4 December at a construction site by the liberation army – the armed wing of the domestic separatist movement known as OPM.

Indonesia said the victims were civilian workers but the OPM – which has not been known historically to target civilians – maintains all were TNI.

The deputy secretary-general of the OPM, Octo Mote, told Radio NZ his was a “professional military organisation”.

“Direct or indirect, these, the ones that were killed are related to military,” he said on Monday. “The OPM conducted investigations before they killed them.”

West Papuan separatists have said growing support for their cause among Indonesian nationals has also prompted crackdowns. More than 500 protesters were arrested in 1 December at rallies across the archipelago, including Indonesians, they claim. Further protests have been held this week calling for an end to the Nduga operation.

Indonesian authorities have also raided and destroyed a number of headquarters of the domestic movement, the West Papua National Committee, and at least three people – including the previously imprisoned activist Yanto Awerkion – are facing “rebellion” charges after holding a prayer meeting they had notified authorities about.