The attack near the town of Silvan, in Diyarbakir province, also left seven soldiers injured two of them seriously, according to provincial governor Mustafa Toprak.
The incident took place during an army operation in the mountainous region known to be a stronghold of the Kurdistan Workers' Party (PKK), and the gunfire continued into the evening, according to the local sources who described the action as a rebel ambush.
The army brought in reinforcements with the help of helicopters and the fierce clashes started a fire in a nearby forest, the sources said.
The United States denounced the attack, which took place as Secretary of State Hillary Clinton was en route to Turkey.
"The United States condemns in the strongest terms" the killings of Turkish soldiers, State Department spokesman Mark Toner told reporters in Washington.
"We strongly support Turkey in its fight against terror and we'll continue to work with the government of Turkey to combat terrorism in all its forms," he said.
According to the Anatolia new agency, Prime Minister Recep Tayyip Erdogan cancelled his engagements in Istanbul to convene an emergency meeting with top security chiefs, including army commanders and interior minister Besir Atalay.
After that meeting, which lasted 45 minutes, Erdogan issued a statement stressing Ankara's determination to subdue the militant rebels.
"The objective of the forces behind this attack are clear. (But) Turkey has the forces and the determination to overcome the terrorism issue," he said.
In parliament, assembly president Cemil Cicek reacted angrily to the latest rebel action, calling on Kurdish leaders to choose their path,
"On the one side there is democracy, peace and freedom, but on the other blood, hate and barbarism," he said in comments run by the Anatolia news agency.
Selahattin Demirtas, head of the biggest pro-Kurdish party in Turkey, the BDP, offered his condolences for the dead Thursday while denouncing the lack of political will to resolve the Kurdish question.
The 36 Kurdish deputies elected to the 550-seat Turkish parliament in last month's polls have refused to take the oath in protest against the detention of fellow Kurds accused of links to the PKK and the invalidation of the election of one deputy due to his prison sentence for "terrorist propaganda".
The attack was the deadliest on the Turkish army since October 2008 when 17 troops were killed in a rebel raid on an army base near the Iraqi border.
Copyright AFP (Agence France-Presse), 2011