The message comes as debate is under way in a number of European countries, most notably France, on whether to ban the Muslim form of dress for women.
The council, which is not related to the European Union, was founded in 1949 to protect human rights and democracy in Europe. It has 47 members, all of whom have signed the European Convention on Human Rights.
Under the convention, limitations on human rights can only usually be justified on the grounds of public health, safety or morals.
Hammarberg added that depending on its terms, a ban might also breach the European Convention on Human Rights.
In January, a French parliamentary report called for a ban on the niqab, saying Muslim women who fully cover their heads and faces posed an "unacceptable" challenge to French values.
Hammarberg said that the small number of women who wear the veil - around 1,900 in France, which is home to Europe's largest Muslim community - made the idea that it undermines democracy, public safety or morals unconvincing.
Women interviewed in the media about why they wore the veil gave a range of reasons, he said.
"There may of course be cases where they are under undue pressure - but it is not shown that a ban would be welcomed by these women," Hammarberg said.
"Rightly, we react strongly against any regime ruling that women must wear these garments. This is absolutely repressive and should not be accepted."
But banning the same clothing in other countries did not remedy this situation, he said, and governments should avoid passing laws on how people dress themselves.
Banning the Muslim veil would be as bad as criminalising the cartoons of Islam's Prophet Muhammad that caused outrage in some Muslim-majority countries when they were published in a Danish newspaper in 2005, Hammarberg added.