Turkey on Thursday blasted as "completely unfounded and untrue" claims that its military used chemical weapons in its fight against outlawed Kurdish militants in northern Iraq.

Media outlets close to the Kurdistan Workers' Party (PKK), which Ankara and its Western allies list as a terror group, claimed that the Turkish army was using chemical weapons in its counter-terror operations.

"The allegations that 'chemical weapons' are used by the Turkish Armed Forces... are completely unfounded and untrue," the defence ministry said, accusing some of seeking to cast a shadow on the army's accomplishments in its fight against the PKK.

Turkish presidential spokesman Ibrahim Kalin slammed the claims as a "lie" and part of a "slander campaign" aimed at the military, police and intelligence who crack down on the fighters.

"The lie of chemical weapons is the futile attempt of those who seek to whitewash and aestheticise terrorism," Kalin tweeted.

Turkish prosecutors launched an investigation into Sebnem Korur Fincanci, head of the Turkish Doctors' Union, after she said she examined video images and claimed that chemical weapons had been used.

"It's obvious that one of the toxic chemical gases that directly affects the nervous system has been used," she claimed.

"Although it is forbidden to use it, we see it is used in clashes."

Fincanci is accused of "making propaganda for a terrorist organisation" and "insulting the Turkish nation and the Turkish state", according to Turkish media reports.

International Physicians for the Prevention of Nuclear War (IPPNW), a non-partisan federation of medical groups in over 60 countries, sent a mission to northern Iraq in late September.

"Some indirect evidence for possible violations of the Chemical Weapons Convention was found," it said in its report.

"Material found near an area abandoned by the Turkish Army included containers for hydrochloric acid and bleach, which could be used to produce chlorine, a classical chemical warfare agent," according to the report.

The PKK has kept up a deadly insurgency for Kurdish self-rule in southeastern Turkey since 1984.

The Turkish army has launched successive operations against the militant group's rear bases in northern Iraq, a persistent thorn in Ankara's ties with the Baghdad government.