President Recep Tayyip Erdogan said Monday that a joint Turkish-Iranian operation against Kurdish militants was "always on the agenda", a week after Tehran's top armed forces commander visited Ankara for rare talks.

Turkey has battled the outlawed Kurdistan Workers' Party (PKK) for decades, while the Iranian security forces have also fought its affiliate, the Party of Free Life of Kurdistan (PJAK). Both groups have rear bases in neighbouring Iraq.

"It is always on the agenda to carry out a joint operation with Iran against those terror organisations which pose a threat," Erdogan told reporters in Istanbul before a trip to Jordan.

- 'Surprise proposal' -

His comments came after Iran's Armed Forces chief of staff General Mohammad Hossein Bagheri visited Turkey last week, with the two sides discussing ways to cooperate against the militants.

During the visit, Iran made a "surprise proposal" to Ankara to launch a joint operation against Kurdish militants in northern Iraq's Kandil and Sinjar regions, the Turkish newspaper Turkiye reported on its front page on Monday.

The newspaper claimed the proposal sparked surprise in Ankara because Turkish officials had long complained that Tehran had left Turkey alone in its fight against the PKK's cadres, financial structuring and political activities.

The PKK is designated as a terror group by Turkey, the European Union and the United States.

Erdogan did not say where the operation would be focused, although the question he was posed related to the Turkiye report on Iraq. He confirmed that the two countries' military chiefs discussed how to work against Kurdish militants.

"The work will continue because you know that the PKK terror organisation has a foot in Iran," he said.

"They always cause harm to Iran and to us. We work because we believe that if the two countries cooperate, we can reach a conclusion in a much shorter period of time," he said.

"I hope that we will get a successful result there," he added, without offering further details on the timing or scope of the operation.

Relations between overwhelmingly Sunni Muslim Turkey, a secular state, and the mainly Shiite Islamic Republic of Iran have on occasion been tense in the last years.

Turkey and Iran lie on opposing sides of the Syrian conflict, with Erdogan seeking the ouster of President Bashar al-Assad to end the war. Tehran, along with Moscow, remain the Syrian leader's key allies and backers.

Erdogan has sometimes lashed out at the rise of "Persian nationalism" in the region, especially concerning the power of Shiite militias in Iraq.

- 'Good agreements' -

Consequently, Bagheri's visit -- which saw him meet both Erdogan and Turkey's top general Hulusi Akar -- was seen as a key moment for bilateral relations.

Bagheri said in comments Monday that during his visit it was agreed that Turkey would step up the control of its border with Iran.

"The actions of Turkey and Iran complement themselves. We reached good agreements to prevent terrorists passing from one side of the border to the other," he said. 

Turkey has already begun building a "security wall" along part of its border with Iran, regional officials said this month, along the lines of a similar barrier on the Syrian border.

Bagheri added that both sides were also united in opposition to a plan by the leadership in Iraq's autonomous Kurdish region to hold a referendum on independence on September 25.

Such geographical changes "could provoke tensions and clashes inside Iraq and would not be limited to that country," Bagheri added.

Widely seen as the world's largest stateless people, most Kurds are spread between Iran, Iraq, Syria and Turkey. But it is only in Iraq where they have achieved a recognised autonomy.