Russia's foreign minister has ruled out holding fresh talks in Geneva to defuse the Ukraine crisis, unless pro-Russian opposition groups are involved.
Sergei Lavrov added there was no point as an April accord between the US, EU and Russia had not been implemented.
He spoke after a Council of Europe meeting which was expected to support Ukraine's plans for a 25 May election.
But Mr Lavrov called an election "unusual" at a time when the army was being used against the population.
Ukraine was ready to back a new round of talks in Geneva, acting Foreign Minister Andriy Deshchytsia said, as long as Moscow supported presidential elections.
He later appealed for international observers to be sent to Ukraine to monitor the May election.
OSCE Chairman Didier Burkhalter said there should be a ceasefire in Ukraine ahead of the poll - as holding it was very difficult in the current situation, the AFP news agency reports.
In other developments in Ukraine:
- Interior Minister Arsen Avakov said on Tuesday that four soldiers and an estimated 30 separatists had been killed in an "anti-terrorism operation" in the eastern town of Sloviansk, where in recent days security forces launched a crackdown on pro-Russian separatists, triggering clashes
- In the southern port of Mariupol, where the city council building was seized a week ago by pro-Russia militants, there were reports of gunfire near a military base close to the city's airport, local media reported. Tyres were set on fire in the centre, giving off thick smoke, they said
- Many flights in and out of Donetsk were suspended. The Ukrainian aviation authorities gave no reason
- New checkpoints were earlier set up around the capital, Kiev. The interior ministry said it wanted to prevent the movement of weapons and explosives
- The authorities also attempted to re-establish control over Odessa, with Interim President Olexander Turchynov dismissing the acting head of the regional administration. Some 46 people died in the Black Sea city on Friday in a fire
At a news conference in Vienna on Tuesday, Mr Lavrov said holding further international talks on Ukraine would be like "going round in circles".
Instead, the government in Kiev and its Western backers needed to implement the steps to resolve the crisis agreed in Geneva last month, he said.
These involved all parties, including the separatists in eastern Ukraine, refraining from violence, vacating occupied buildings and being disarmed in return for an amnesty.
The 25 May presidential election was called after pro-Kremlin President Viktor Yanukovych was overthrown by pro-Western protesters in February.
"Scheduling an election during a time when the army is being used against a part of the population is not conventional - it's not Afghanistan," Mr Lavrov noted.
Earlier, French President Francois Hollande warned there would be "chaos and the risk of civil war" if the election did not take place.
Kiev has rejected the pro-Russian activists' demands for greater autonomy for eastern regions, fearing they could lead to the break-up of the country or more regions being annexed.
Separatists in Donetsk have proclaimed a "People's Republic" and are preparing to hold an independence referendum on Sunday.
US Secretary of State John Kerry called the plan "contrived and bogus", and said the US rejected it as an "illegal effort to further divide Ukraine".