Nepalese migrants building the infrastructure to host the 2022 World Cup have died at a rate of one every two days in 2014 – despite Qatar’s promises to improve their working conditions.

The figure excludes deaths of Indian, Sri Lankan and Bangladeshi workers, raising fears that if fatalities among all migrants were taken into account the toll would almost certainly be more than one a day.

The Nepalese foreign employment promotion board said 157 of its workers in Qatar had died between January and mid-November this year – 67 of sudden cardiac arrest and eight of heart attacks. Thirty-four deaths were recorded as workplace accidents.

Figures sourced separately by the Guardian from Nepalese authorities suggest the total during that period could be as high as 188. In 2013, the figure from January to mid-November was 168.

“We know that people who work long hours in high temperatures are highly vulnerable to fatal heat strokes, so obviously these figures continue to cause alarm,” said Nicholas McGeehan, the Middle East researcher at Human Rights Watch.

“It’s Qatar’s responsibility to determine if deaths are related to living and working conditions, but Qatar flatly rejected a DLA Piper recommendation to launch an immediate investigation into these deaths last year.”

Some within Qatar suggest the cardiac arrest death rates could be comparable to those among Nepalese workers of a similar age at home. The Indian embassy argued this year that the number of deaths was in line with the average in their home country. But in the absence of robust research or any attempt to catalogue the cause of death, human rights organisations say it is impossible to properly compare figures.