TUNCELI, Turkey, May 31 (Reuters) - Turkish soldiers have killed three Kurdish guerrillas in a clash in eastern Turkey, security sources said on Thursday. The firefight, during an operation in the mountainous province of Tunceli, came amid grow speculation about a possible military incursion by Turkish forces into northern Iraq to destroy Kurdish rebel bases there. The Tunceli operation, which began on Wednesday, was continuing across the province on Thursday against militants from the Kurdistan Workers Party (PKK). Several dozen PKK guerrillas have been killed in clashes with troops in the last two months as more rebels cross high mountains from northern Iraq to battle Turkish forces amid rising spring temperatures. Security forces killed 10 PKK fighters in clashes across the southeast on Tuesday. Iraqi Kurdish leaders have repeatedly warned Turkey against carrying out incursions on their territory and the United States has also reacted coolly to the prospect of any cross-border operation into Iraq. More than 30,000 people have been killed in the conflict since the PKK took up arms in 1984 with the aim of creating an ethnic homeland in the southeast of the country.