President Tayyip Erdogan said Turkey’s armed forces have never used chemical weapons and they abide by international law, saying legal action would be taken against those who have made allegations on the issue, broadcaster NTV reported on Friday.

“Our armed forces have not resorted to using chemical weapons to this day,” NTV cited Erdogan as telling reporters on his plane returning from a trip to Azerbaijan. “They will always cast such slanders. We will call them to account as is required within the law.”

Media close to the Kurdistan Workers Party (PKK) militant group published videos this week that it said showed chemical weapons being used by the army against the PKK in northern Iraq.

Separately, an international medical groups’ federation published a report this month seeking an independent investigation of possible violations of the 1997 Chemical Weapons Convention.

On Thursday Turkey’s defence ministry firmly denied the allegations.

“Allegations that ‘the Turkish Armed Forces used chemical weapons’ are completely baseless and untrue,” the defence ministry said in a statement.

“All these disinformation efforts are the futile struggles of the terrorist organization and its allies,” it said, adding that ammunition prohibited by international law and agreements was not used by, or in the inventory of, its armed forces.

The PKK is designated a terrorist group by Turkey, the European Union and the United States.

“The chemical weapons lie is a futile attempt by those who try to whitewash and airbrush terrorism. Our fight against terrorism will continue with resolve and determination,” presidential spokesman Ibrahim Kalin said on Twitter.

Omer Celik, spokesman of President Tayyip Erdogan‘s ruling AK Party, described those who make chemical weapons’ allegations as part of “a vile slander network”.

International Physicians for the Prevention of Nuclear War (IPPNW), which represents thousands of doctors and campaigns to prevent armed violence, said it found indirect evidence of possible violations during a September mission to northern Iraq.

In its report, the IPPNW said Defence Minister Hulusi Akar openly acknowledged in Turkey’s parliament last year the use of tear gas during an operation against the PKK in northern Iraq.

“This is an outright violation of the Chemical Weapons Convention and should be pursued legally by the international community,” it said.

The IPPNW said it found in northern Iraq material near an area abandoned by the Turkish army including containers for hydrochloric acid and bleach, which could be used to produce chlorine, a chemical warfare agent. At the same site containers were found for gas masks protecting against chemical weapons, it said.

It said none of its evidence was definitive proof of chemical weapons use but it warranted further independent investigation.