MPs in Turkey are debating a motion authorising cross-border military operations into northern Iraq to target Kurdish rebel bases there.
Turkey has begun preparations for a cross-border operation
Parliament in Ankara is expected to approve the motion by a large majority amid widespread public support for military action against the PKK.
Turkey is responding to recent attacks it blames on the rebels.
But Iraqi leaders and the US have urged Turkey to show restraint, fearing any action could destabilise northern Iraq.
The autonomous Kurdish regional government in northern Iraq warned Turkish MPs that any intervention would be "illegal". It has denied helping the PKK.
The rebels themselves said they would meet force with force.
The parliamentary motion says that Turkey has warned Iraq repeatedly to clamp down on the PKK, to no avail.
However, Iraqi Prime Minister Nouri Maliki called his Turkish counterpart on Wednesday, saying he was "absolutely determined" to remove the PKK from Iraq and pleading for more time, according to the Anatolia news agency.
Iraqi Vice-President Tareq Hashemi has also been visiting Ankara.
"The Iraqi government should be given a chance to prevent the cross-border terrorist activities," Turkish media quoted him as saying.
Meanwhile, Nato Secretary General Jaap de Hoop Scheffer entered the debate by telephoning Turkish President Abdullah Gul to urge restraint.
"He expressed his view that all parties should exercise the greatest possible restraint, particularly in this time of great tension," a Nato spokesman told a regular news briefing on Wednesday.
The recent death of 13 Turkish soldiers in an ambush blamed on the PKK has put the government under renewed pressure to respond with force.
Prime Minister Recep Tayyip Erdogan has said the motion does not mean a military operation is imminent.
But he also warned that Turkey would act decisively in its fight against terrorism.
The chief of the rebels' executive council, Murat Karayilan, told the Kurdish Hawlati newspaper: "Thousands of PKK guerrillas are on standby to fight Turkish army forces."
The PKK wants more autonomy in south-eastern Turkey
Meanwhile Syrian President Bashar Assad, visiting Turkey, said he supported the country's right to take the action "against terrorism and terrorist activities".
Turkey is a regional hub for the US military, and some suggest access to Incirlik airbase or other supply lines crucial to US forces in Iraq and Afghanistan could be affected by the row.
The US is also at odds with Turkey over a planned Congressional vote to recognise the mass killing of Armenians in Ottoman times as genocide, although support for that resolution on Capitol Hill now appears to be waning.
Key Democrats in the US House of Representatives have joined Republicans to warn that US strategic interests could be damaged by the largely symbolic resolution, which US President George W Bush strongly opposes.
BBC world affairs correspondent Nick Childs says the stakes for any Turkish military action on Iraqi soil are potentially very high.
An incursion posing a threat to the oilfields around Kirkuk could provoke a major crisis, which might suck in Iraqi forces, the Americans and maybe even the Iranians, he says.
Iraq and America are concerned military action will bring chaos to the only relatively calm region of Iraq, he adds.
The head of the UN refugee agency has said he is deeply concerned Turkish action could lead to big displacements of people.