Vladimir Putin said on Wednesday he hoped talks between Russia, Ukraine, the EU and US due next week would have a "positive" outcome, but warned that Ukraine's interim government should not do anything that could not "be fixed later".
The four-way talks, the first since the crisis, were announced on Tuesday night.
"I hope that the initiative of Russian foreign ministry on adjusting the situation and changing it for the better will have consequences, and that the outcome will be positive," the Russian president told a televised government meeting. "At the very least, I hope that the acting [leaders] will not do anything that cannot be fixed later."
John Kerry, the US secretary of state, and Sergei Lavrov, Russia's foreign minister, discussed the meeting on the phone on Wednesday, according to the Russian foreign ministry. It said the two men had urged all sides to refrain from violence in eastern and southern Ukraine.
But diplomats said it was unlikely the talks would produce any major breakthroughs, given Russia and the west viewed the situation in Ukraine so differently, with both sides accusing the other of stoking tension.
"We don't have high expectations for these talks, but we do believe it is very important to keep that diplomatic door open," said Victoria Nuland, the US assistant secretary of state.
The situation in the east of Ukraine is tense, with Ukrainian authorities promising on Wednesday morning to end the occupation of administrative buildings by pro-Russian separatists within 48 hours, either by negotiations or force.
"A resolution to this crisis will be found within the next 48 hours," said Arsen Avakov, interior minister, in Kiev, referring to the eastern cities of Luhansk and Donetsk where protesters remain in control of government buildings.
"For those who want dialogue, we propose talks and a political solution. For the minority who want conflict, they will get a forceful answer from the Ukrainian authorities," he said.
A group of pro-Russian protesters calling themselves the Army of the Southeast were occupying the security service headquarters in Luhansk. Members of the building's defence who identified themselves as former Berkut (special police) officers from other regions, said they would not fire first but if attacked would fight back until Russian forces arrived.
The Kremlin has said it is prepared to intervene as in Crimea to protect ethnic Russians in other parts of Ukraine, amid reports of a Russian troop buildup along the border.
The masked commander said the security service building's defence included him and 42 other former members of the elite Alpha division of the now-disbanded Berkut, who were known as former president Viktor Yanukovich's shock troops during the Euromaidan protests in Kiev. He said the former president, who fled to Russia in February, had betrayed them.
A few hundred demonstrators stood in the square in front of the building, protesting against the new regime in Kiev, which many said had been installed by the US government.
Tatiana Pogukai, a spokesperson of the Luhansk division of the interior ministry, told the Guardian that a group of security service and law enforcement officials and politicians continued to negotiate with the occupiers, who are demanding a referendum on "the region's economic independence from Kiev".
Kiev has claimed the protesters are directed by Russian security services, and, on Tuesday, Kerry accused Moscow of stirring up unrest, possibly as a pretext for Crimea-style military intervention.
There are concerns about the new government in Kiev, but support for actually joining Russia is not widespread among the population, unlike in Crimea.
In Moscow, Putin met the cabinet on Wednesday and discussed possible economic responses to Ukraine. Gazprom, the Russian gas monopoly, says it has not received any money for March gas deliveries to Ukraine and still has a $2.2bn (£1.6bn) debt outstanding. Kiev has said it will pay the debt but has protested at an 80% increase in gas prices announced last week.
Putin said it was possible that Russia could make Ukraine pay up front for deliveries of gas, but he instructed the government to wait until "further consultations" with Kiev before introducing the measure.
The gas dispute is another way for Moscow to put pressure on Kiev, and is likely to be another issue at the talks next week, which will be the first four-way meeting since Viktor Yanukovych fled Ukraine and the new government was formed.
Since then, Russia has annexed Crimea, and Kiev and Moscow have been engaged in a bitter war of words, with both sides accusing the other of sponsoring terrorism.
The Kiev government claimed it had evidence that Russian security services were behind the violence that left more than 100 dead in Kiev in February, while Russian security services say they have arrested a number of Ukrainians acting on official orders and planning terror attacks inside Russia.
