DIYARBAKIR, Turkey (Reuters) - Four Turkish soldiers were killed on Sunday in two separate clashes with militants of the outlawed Kurdistan Workers Party (PKK), officials said.

In the first incident, the militants opened fire on soldiers in a forested area of Ordu province in northeast Turkey, killing three and injuring two others, the provincial governor, Irfan Balkanlioglu, said in a statement.

Large numbers of reinforcements were sent to the area and operations are continuing, he added.

In a separate incident, PKK fighters killed one soldier and injured six others during a security operation in a remote corner of Hakkari province in southeast Turkey near the borders with Iran and Iraq, security sources said.

The latest deaths came one day after the Turkish army killed 35 militants when they tried to storm a base in Hakkari province.

Thousands of militants and hundreds of civilians and soldiers have been killed since a 2-1/2-year ceasefire and peace process between the government and the PKK broke down last July.

More than 40,000 people have been killed in the conflict since the PKK - designated a terrorist group by Turkey, the United States and the European Union - began its insurgency in 1984.

Turkey's military, NATO's second largest, is currently undergoing a major shake-up following a July 15-16 coup attempt, but has played down concerns that the wide-reaching changes will undermine its struggle against the PKK.

(Reporting by Seyhmus Cakan; Writing by Gareth Jones; Editing by David Dolan)