By Sarah Rainsford BBC News, Istanbul

Archive images of US jets over north Iraq show the difficult terrain

It does appear to be a limited operation, and the target is close to Turkey's border.

It follows the first air strikes by Turkish fighter jets over the weekend - on targets in the Kandil mountains, far deeper inside Iraqi territory.

"If reports of this operation with ground troops are true, then it reflects an opportunity that was seized," believes retired Brig-Gen Haldun Solmazturk.

He says 300 soldiers is not an unusual number for such an operation, in which he suspects the military was pursuing a PKK target, spotted just across the border.

"These are called 'targets of opportunity'," he says.

"Once the enemy has been spotted, no-one would want to miss the opportunity to act."

Psychological value

Turkey has been threatening military action against the PKK ever since insurgents intensified their attacks on Turkish troops, putting the government here under immense public pressure to respond with force.

A full incursion which would destabilise northern Iraq will not be allowed Hasan Koni Bahcesehir University, Istanbul

Last month, the government authorised the military to carry out cross-border operations against the PKK whenever necessary.

The air strikes on Sunday night were the first serious sign of that.

The military says its still assessing the physical impact, but most analysts agree the main aim of the operation was psychological. On Monday, local media hailed it as a success.

"I believe the area targeted was already almost empty," says Hasan Koni of Istanbul's Bahcesehir University.

"It's winter so the PKK would already be down in the villages.

"But the Turkish people have been waiting for an operation, and this will calm them. Also the Turkish army is proving it can mount an incursion, and it has the support of the USA."

A statement from the office of the General Staff said its initial assessment suggests targets were struck with "perfect accuracy".

It says only the target area was hit, following confirmation it was not populated by civilians.

'US intelligence'

However, the UN refugee agency reports the displacement of 1,800 people following the bombing at the weekend, and says it is "very concerned". Reports suggest one civilian was killed.

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Ankara says it has tacit approval from the US for its operations, under an agreement reached in Washington last month by Prime Minister Recep Tayyip Erdogan and President George W Bush.

"I believe the USA supplied actionable intelligence, and the Turkish military took action," Turkish foreign ministry spokesman Levent Bilman told the BBC.

He declined to comment on reports of a more recent ground incursion.

"The USA was not asked for approval [for the air strikes] because that is not needed.

"It is up to us to decide when to act and how. The US was notified."

He said Turkey would continue to act on the basis of intelligence received.

Small for now

"I believe operations will continue on this scale - pin-point operations, hot-pursuit raids and carefully controlled air strikes," agrees retired Brig Gen Solmazturk.

"This approach has to be maintained to have an impact. But I don't see any possibility of a larger-scale incursion at this point. The conditions are not there."

The US remains firmly opposed to any major cross-border incursion into the only relatively stable region of Iraq.

"These point-operations and air strikes are permitted," says Hasan Koni.

"But a full incursion which would destabilise northern Iraq will not be allowed, I believe.

"Everybody knows that and Turkey accepts it. Nobody can confront the US - nowadays especially."