France’s health minister has announced a new investigation into the births of several babies with upper limb defects in various parts of the country in recent years, saying it was “unacceptable” no cause had been found.

Agnès Buzyn said she and her environment counterpart, François de Rugy, had decided to look more closely at what caused 14 babies to be born with stunted or missing arms since 2007, two weeks after health authorities said they had failed to find an explanation.

The cases have been concentrated in three French “departments” or administrative areas – Ain near the Swiss border, which had seven cases between 2009 and 2014, Brittany on the west coast, which had four cases between 2011 and 2013, and Loire-Atlantique, south of Brittany, which had three cases in 2007-2008.

In a 4 October report, France’s public health agency said that while the number of cases in the Ain area were not above the national average the numbers in Brittany and Loire-Atlantique were statistically excessive.

But it said it found no “common exposure” to substances that could explain them.

Fewer than 150 babies are born each year in France with upper limb defects, which occur when part of the arm or the entire limb fails to form completely during pregnancy.

While the cause of the defects are unknown, research has shown that exposure of the mother to certain chemicals or medication during the pregnancy can increase the risk.

Buzyn told the LCI channel that environmental experts would now join health experts in investigating the cases to try to shed light on the phenomenon.

“We cannot content ourselves with saying we didn’t find the cause, that’s unacceptable,” she said.

In the 1950s and 1960s, thousands of babies around the world were born with missing or stunted limbs linked to the use of the drug thalidomide, which was used to treat nausea in pregnant women. It was banned in the 1960s.