ISTANBUL (Reuters) - President Tayyip Erdogan said on Monday Turkey has evidence that mayors removed from two dozen Kurdish-run municipalities had sent support to Kurdish militants, and said they should have been stripped of office sooner.

Turkey appointed new administrators in the 24 Kurdish-run municipalities on Sunday, triggering pockets of protest in parts of the largely-Kurdish southeast. The main pro-Kurdish opposition party called it an "administrative coup".

"It is a step taken too late in my opinion. It should have been taken sooner, and it was my advice to do so earlier," Erdogan told reporters in Istanbul after attending prayers to mark the Muslim Eid al-Adha holiday.

"They sent the support they received to the mountains, but this has all been discovered," Erdogan said, referring to Kurdish militant bases in the mountains of southeastern Turkey and northern Iraq. "Our government took this decision based on all of this evidence."

Erdogan said last week that the campaign against the Kurdistan Workers Party (PKK) militant group, which has waged a three-decade insurgency for Kurdish autonomy, was now Turkey's largest ever and that the removal of civil servants linked to them was a key part of the fight.

The 24 municipalities had been run by the pro-Kurdish opposition Peoples' Democratic Party (HDP), the third largest in parliament, which denies direct links to the militants. It said it did not recognize the legitimacy of the mayors' removal.

The U.S. embassy said on Sunday that while it supported Turkey's right to combat terrorism, it hoped the appointment of government administrators would be temporary and that local citizens could soon choose new representatives.

The United States and European Union both list the PKK as a terrorist organization.

(Reporting by Tuvan Gumrukcu; Writing by Nick Tattersall; Editing by Dominic Evans)