(Adds operation in Turkey, background)

ISTANBUL, March 29 (Reuters) - Turkey's armed forces killed 15 members of the outlawed Kurdistan Workers Party (PKK) in northern Iraq on Thursday using long-range land weapons, and then followed up with air strikes, they said on Saturday.

It was the first time Turkish forces had killed a group of Kurdish rebels inside northern Iraq since the end of a large-scale ground incursion into the neighbouring country last month, according to information given by the armed forces.

The General Staff said on its website that the militants were trying to cross into Turkey, where they planned an attack.

The army fired on the separatists with long-range weapons, killing 15, and then launched air strikes in the same area of northern Iraq on Friday. It was unclear how many had been killed in the air strikes.

On the other side of the border on Saturday, troops pursued rebels in the mountainous province of Sirnak, backed up by attack helicopters, security sources said.

Turkish warplanes and artillery have periodically bombed and shelled PKK positions in northern Iraq over several months, helped by intelligence provided by U.S. forces in Iraq.

On Feb. 21, the military launched a major ground incursion against the PKK, sending thousands of troops into Iraq. The General Staff says 240 rebels were killed in the week-long campaign, along with 27 of its own men.

The cross-border operation prompted concern in Washington about further regional instability and was watched closely in Turkey's financial markets.

Turkey blames the PKK for the deaths of nearly 40,000 people, mostly Kurds, since the group began its armed campaign for an ethnic homeland in southeast Turkey in 1984. Turkey, like the European Union and United States, considers the PKK a terrorist organisation. (Reporting by Emma Ross-Thomas; Editing by Richard Balmforth)

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