NGOs in Pakistan say the death of at least 132 children in a drought in Sindh province might have been avoided had the government responded sooner. As government aid begins to arrive in the area, local activists have linked the crisis to long-term failures to provide proper health care and infrastructure in the region.

The deaths occurred in the Thar desert, part of Tharparkar district, some 350km (200 miles) from Karachi, which runs up to the border with India.

Local organisations working with some of the poorest people in the area claim many of those affected by the drought are members of the Dalit caste. Known in Pakistan as the scheduled class, Dalits suffer heavy discrimination under the caste system common across south Asia.

According to the Pakistan Dalit Solidarity Network (PDSN), "animals started dying in the desert in October last year but the government didn't act until reports of children dying in the Mithi taluka hospital."

Hospital sources told the media last week that 38 children died of malnutrition in the Mithi taluka hospital in December. There were more deaths in the first three months of 2014, including those of three children on Monday.

The chief minister of Sindh, Syed Qaim Ali Shah, has ordered an inquiry into the delay in distributing relief to people in Tharparkar.

The severe drought was caused by below average rainfall during last year's monsoon season. However, some experts believe there are deeper, structural reasons for the severe malnutrition suffered in the region. "Malnutrition is not just limited to Tharparkar, the situation in the entire Sindh province is alarming," says Arif Jabbar Khan, Oxfam's country director for Pakistan. "57% of children under the age of five are stunted and 72% of households are food insecure."

When rainfall is below average, the region usually recieves subsidised food and animal fodder by August. This time, however, the chief minister did not begin relief efforts until November.

On a visit to the drought-hit area, Nawaz Sharif, the prime minister, announced a 1 billion Pakistani rupee aid package (£6.15m) and ordered an investigation into corruption in wheat distribution.

The remote district, which has a population of about 1.5 million people, consists of more than 2,000 small villages. Health infrastructure is poor and there are few road links to more developed parts of Pakistan. Poverty is high and food scarce.

Javed Jabbar, the founder of Baanhn Beli, a non-governmental organisation that has been working in Tharparkar since 1985, believes there should be a non-partisan inquiry into the failure to react more quickly to signs of the building crisis: "Elected representatives must be held responsible for not reporting to the chief minister."

He believes a lack of investment in health in the region is partly to blame for the deaths, pointing to long-standing vacancies in government-run hospitals and rural centres. "The Nawabshah Medical College is an all women's college, and yet there are just a handful of female doctors working in Nagarparkar. I think those who study medicine should be made to sign a bond that after completion of their studies they will serve in these difficult areas, especially women. The root cause of this crisis is maternal health which has a direct bearing on the infant health."

"Malnutrition is not a new or sudden phenomenon, and neither is drought, but it had remained under the radar for too long," says Dr DS Akram, a paediatrician who has been working in the region since the 1990s.

Oxfam say that there is no shortage of food. According to Khan, "Missing public policy action and persistent economic inequalities are the main causes of malnutrition, which – if not addressed – may aggravate the situation in future in the entire province."

Campaigners are concerned that lack of long-term development in the area has a disproportionate impact on the Dalit community. Because of the remote nature of the affected region, it is difficult to know with complete certainty how many have died. The PDSN's Dr Sono Khangarani believes the true number may be as high as 190: "Not everyone brought their children to the hospital, one cannot give an exact figure. But since most deaths are of children belonging to the poorest of the poor, one can conclude the children belong to Dalits."

Drought in the wider area is not a recent phenomenon. There have been periods where there has been insufficient rains for several years in a row. In 2010 floods hit the Sindh region, part of a pattern of extreme weatherseen across Pakistan in recent years.

The Sindh region, like the rest of Pakistan, faces environmental uncertainty. Even 15 years ago, experts were warning that persistent drought in Pakistan was shrinking the country's GDP because of poor agricultural performance. Last summer, leading meteorologists warned that the country can expect longer, more intense and more frequent weather events in the future.

On Tuesday evening, the Sindh government changed the brief of the relief and revenue minister Makhdoom Jamiluz Zaman. He will continue as revenue minister only. Taj Haider, a senior Pakistan People's Party leader, is now the relief commissioner.