The Indian government has made it compulsory for cough syrup makers to get samples tested before exporting their products.

Starting 1 June, these companies will have to get a certificate of analysis from a government-approved laboratory.

The rule change comes after some Indian-made cough syrups were linked to deaths in The Gambia and Uzbekistan.

The controversies had cast a pall over India's pharmaceutical industry, which makes a third of the world's medicines.

The announcement was made by the Director General of Foreign Trade, which said in a notification that cough syrups would be permitted to be exported "subject to the export sample being tested".

It also mentioned a list of central and state government laboratories across the country where samples could be tested.

Last week, Reuters had reported that India was considering a policy change after domestic cough syrups were linked to child deaths abroad.

Many Indian pharma companies have come under scrutiny for the quality of their drugs, with experts raising concerns over their manufacturing practices.

In March, India's drug regulator cancelled the manufacturing licence of Marion Biotech, whose cough syrups were linked to 18 child deaths in Uzbekistan.

The World Health Organization also issued an alert in October linking four Indian-made cough syrups to child deaths in The Gambia.

India later said that the medicines complied with specifications when tested at home, but the WHO responded that it stood by "the action taken".