The plan aims to expand a ceasefire in the city of Aleppo, brokered by Turkey and Russia earlier this month to allow the evacuation of civilians, to all of the country, the state-run Anadolu news agency said.
Like previous ceasefire plans that had been brokered by the United States and Russia, it excludes "terror" groups, the agency said.
A Syrian rebel source, who asked not to be named, told AFP in Beirut that details still had to be submitted to the rebel groups and said there was no agreement as yet.
Turkey's Foreign Minister Mevlut Cavusgolu said a transition towards peace in Syria that involves President Bashar al-Assad is "impossible" as the country's opposition will not accept him.
Cavusgolu also confirmed Turkey had prepared an agreement towards a ceasefire.
There was no immediate official confirmation of the plan from Moscow.
"I cannot answer that question right now," Kremlin spokesman Dmitry Peskov told reporters on a conference call. "I don't have sufficient information."
"We are constantly in touch with our Turkish colleagues to discuss various details about the possible talks that are planned for Astana," he said, referring to potential Syrian peace talks Russia wants to organise in Kazakhstan.
"This is all being done to search for a political resolution for Syria."
If successful, the new plan will form the basis of upcoming political negotiations between the Damascus regime and opposition overseen by Russia and Turkey in the Kazakh capital Astana, it added.
Turkey and Russia will work for the plan to come into force at midnight, the agency said, without giving further details.
It was not immediately clear how and where the plan had been agreed but there have been talks in the last weeks between Turkey, Russia and Syrian opposition representatives in Ankara.
Qatar-based channel Al-Jazeera said a new meeting is planned on Thursday in Ankara, this time between military representatives of Syrian rebels and Russia.
Heading to Astana?
Ankara and Moscow have been on opposing sides in the Syrian civil war, with Turkey seeking the ouster of President Bashar al-Assad and Russia, along with Iran, his key international ally.
But the two countries have started in the last months to cooperate more tightly on Syria, especially after a deal in summer to normalise ties battered by Turkey's shooting down of a Russian warplane last year.
Ankara remained conspicuously quiet as Assad's forces, backed by Russia, took control last week of all of Aleppo in the biggest defeat for the rebels in the civil war so far.
No date has yet been set for the Astana talks and Russian foreign ministry spokesman Maria Zakharova said the meeting was still at the planning stage.
She emphasised that the talks were not intended to replace the peace process based in Geneva which has sought to find a solution for the Syrian conflict.
But the direct bilateral involvement of Turkey and Russia comes as Turkish President Recep Tayyip Erdogan is increasingly expressing impatience at the role of the United States in Syria.
Previous ceasefire plans had been brokered by US Secretary of State John Kerry and Russian counterpart Sergei Lavrov. They met with only temporary success and failed to lead to a solution for the conflict.
It remains unclear how the latest ceasefire plan will apply to the Fateh al-Sham, formerly the Al-Qaeda affiliate Al-Nusra Front, which has worked more closely with the rebels since changing its name.
'No going back'
Erdogan had on Tuesday launched one of his most bitter attacks yet on US and Western policy in Syria, which he said was marked by broken promises.
He accused the West of not just supporting Kurdish militia that Ankara regards as a "terror group" but even Islamic State (IS) jihadists.
Turkey has been enraged by the US policy of using the Kurdish Peoples' Protection Units (YPG) as a trusted ally on the ground against IS. To Ankara's pleasure, Russia has steered clear of overt cooperation with the YPG.
The Turkish strongman accused the West of failing to back Turkey's own incursion inside Syria in support of pro-Ankara fighters to oust IS from the border area, which has taken increasing casualties in recent weeks.
But he vowed: "There is no going back on the path we have set out on."
Backing the talks in Astana, Erdogan was dismissive of the Geneva process. "Unfortunately, Geneva came up empty. How many meetings were held? And no results were obtained," he said.
In continued bloodshed, air strikes carried out by unidentified aircraft killed at least 22 civilians, including 10 children, in a village held by IS in Deir Ezzor province, the Syrian Observatory for Human Rights said.
The Syrian civil war, which began in 2011 as an uprising against Assad, has now lasted nearly six years and killed more than 310,000 people.
Air strikes kill 22 civilians in eastern Syria
Air strikes carried out by unidentified aircraft have reportedly killed at least 22 civilians, including 10 children, in a village held by the Islamic State group in eastern Syria.
The Syrian Observatory for Human Rights said the civilians were from two families at Hojna in Deir Ezzor, which borders Iraq and is the country's second biggest province after Homs.
The oil-rich province of Deir Ezzor is almost totally under IS control and has been regularly targeted by a US-led military coalition.
The only part of the eastern province outside of IS control is its capital, which is also named Deir Ezzor and is held by forces loyal to Syrian President Bashar al-Assad.
The Turkish military have also released a statement saying it, wounding 117 others, in an operation in al-Bab.
IS has carried out a series of attacks across Europe and has been targeted by military offensives on several fronts in Syria and Iraq, where it declared an Islamic "caliphate" in 2014.
In Syria, IS is targeted by warplanes of the US-led coalition as well as Turkey, the Syrian regime and its ally Russia in the northern province of Aleppo, Deir Ezzor and its stronghold of Raqa.
