The report, published Thursday, quotes a study saying that levels of endocrine disease and blood disorders in polluted areas are twice the regional average.

The study was conducted by a team of Russian scientists led by epidemiologist Sergei Zykov.

"No direct influence of space-related activities on the population's health has so far been established," the Russian space agency said in its response.

The study quoted by Nature focussed on children in the Altai Republic, a mountainous region on the southern fringes of Siberia.

This area was chosen because of pollution from unburnt fuel, notably hydrazine, which is used to power the early stages of some Russian launchers.

Zykov compared the health records of about 1,000 children in two polluted areas for 1998-2000, comparing them with 330 records from a nearby unpolluted control group.

He concluded that children in the worst-affected areas were up to twice as likely to need medical attention during this time, and needed to be treated twice as long, Nature said.

According to Zykov's calculations, dozens of litres (several gallons) of unburned fuel are sprayed over several square kilometers (miles) of land with every launch.

The Russian space agency said in its statement that since 1998 it had been conducting "researches to examine the influence of space-related activities on the environment and the health of the population" living near zones where fragments of Russian launchers regularly come down to Earth.

It hinted that health problems among local children might have another cause than rocket launching and might go back to Soviet-era nuclear tests carried out in the vicinity.

"Some of those areas (surveyed in the study) are officially considered as zones influenced by the Semipalatinsk nuclear testing range," the agency said.

Over 500 nuclear explosions were carried out over 40 years at Semipalatinsk, now located in northeastern Kazakhstan. The facilities were closed down in 1991, in the final days of the Soviet Union.

However, the agency stopped short of saying rocket fuel was totally harmless.

"There are no grounds for replacing the launchers' fuel with another (kind of fuel), as all other kinds of fuel also harm the environment," it said.

The Baikonur Cosmodrome is run by the Russian space agency Rosaviakosmos but both NASA and the European Space Agency pay to have craft launched from there.

All rights reserved. copyright 2018 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.