The main Kurdish militia in Syria confirmed it will take part in a ceasefire brokered by the US and Russia meant to go into effect on the weekend, but Turkey said it reserved the right to take action against the group.
The People's Protection Units (YPG) attach "great importance" to the deal, spokesman Redur Xelil said Thursday, while reserving the right to self-defence.
Turkish Prime Minister Ahmet Davutoglu, whose military has been shelling the YPG, said he was reserving the right to take security measures against both the Kurdish militia and Islamic State.
"When it comes to the security of Turkey, this ceasefire is not binding," Davutoglu said.
The "cessation of hostilities" deal goes into effect at midnight Saturday (2200 GMT Friday). Each armed group must sign up by noon Friday indicating their agreement. The Syrian government confirmed its participation this week.
The deal excludes Islamic State, al Qaeda affiliate the al-Nusra Front and other UN listed terrorist groups.
Turkish President Recep Tayyip Erdogan has made clear he wants the YPG excluded from the ceasefire.
The YPG is the main ally of the United States on the ground in Syria fighting against Islamic State. The Kurds have been seizing vast amounts of territory from the extremist group. But Turkey, which fights Kurdish rebels on its own soil, is worried by the gains.
The Syrian Observatory for Human Rights and the pro-Kurdish Firat news agency said Turkey shelled the YPG on Wednesday. Ankara has not presented any proof the YPG has attacked its territory.
Turkey has also launched airstrikes against Kurdistan Workers' Party (PKK) bases in northern Iraq.
Meanwhile, the Southern Front, a coalition of Syrian rebels in the south of the country, said it would adhere to the ceasefire.
Syria's main opposition bloc said late Wednesday that it will support a temporary two-week ceasefire deal.
"The High Negotiations Committee believes that a temporary truce for two weeks would provide a chance to determine the seriousness and commitment of the other side," it said.
The Syrian army has announced that Daraya, an area on the outskirts of the capital Damascus and close to an airbase, will be excluded from the ceasefire agreement, claiming that al-Nusra has a large presence there.
The Southern Front denied this, highlighting how difficult it will be to implement a ceasefire that allows some groups to be targeted. Al-Nusra fights alongside rebels in many areas of the country.
Syrian government forces, meanwhile, said that they have taken full control of the town of Khanasser in the north two days after it fell to Islamic State, state media reported.
The town was the only lifeline to government-held parts of Aleppo. The rebel-held areas of the city, once Syria's economic hub, are preparing for a possible siege by government forces, as it becomes encircled.
The ceasefire deal is meant to help bring aid to besieged areas.
However, the UN failed in its first attempt to parachute aid to Syrians trapped in Deir ez-Zor, as the entire 21 tons of food were lost or destroyed, a World Food Programme (WFP) spokeswoman said.
Most of the parachutes drifted away from their targets, while others failed to open during the Wednesday operation and hit the ground.
Reaching Deir-ez-Zor, which is besieged by Islamic States extremists, is a key goal because the city accounts for nearly half of the 480,000 people living in besieged areas in Syria, senior UN advisor Jan Egeland explained.
Meanwhile, the UN Security Council is expected to meet this week to adopt a motion backing the ceasefire, as special envoy for Syria Staffan De Mistura said he will provide "information regarding the resumption of Geneva talks" on Friday.
The Geneva talks are meant to help guide the country out of war into a transition, but so far efforts to bridge the gap between the government and the opposition, which demands President Bashar al-Assad step down, have failed.