He described violent clashes between anti-government protesters and police as "scary" and accused EU politicians of stirring up the situation.
There has been a second consecutive night of clashes in Kiev.
Young men threw fireworks and petrol bombs at police guarding the road leading up to the Ukrainian parliament.
Police violently beat some protesters.
The violence - which has been restricted to a small area around Hrushevskyy Street - abated on Tuesday morning, but correspondents say there is a widespread expectation that it could resume later in the day.
Mr Lavrov's warning came after Ukrainian President Viktor Yanukovych on Monday cautioned that the violence threatened the country's stability.
An array of new anti-protest laws, hastily passed by parliament last week, will come into force on Wednesday.
Protesters have been camped out in Kiev since late November, angered by the government's turn to Moscow and its rejection of a planned treaty with the EU.
"Members of several European governments rushed to the Maidan without any invitation and took part in anti-government demonstrations in a country with which they have diplomatic ties," Mr Lavrov said, referring to the square in which protesters have been encamped for many weeks.
"This is simply indecent."
He did not name names, but European Union foreign policy chief Catherine Ashton and the then German Foreign Minister Guido Westerwelle visited the protesters in December, as did US Assistant Secretary of State Victoria Nuland.
Warning that the "situation is getting out of control", Mr Lavrov added:
"We have information that much of this is being stimulated from abroad."
Lines of riot police still held the road leading up to parliament on Tuesday morning, behind burnt-out buses and barricades, reports the BBC's Daniel Sandford in Kiev.
Clashes went on through the night, with police using tear gas and stun grenades against several hundred young men ranged against them.
At times, thousands of people cheered from the sidelines.
Eighty police have been admitted to hospital following the most recent clashes, says Ukraine's interior ministry.
It says 32 protesters have been arrested.
Thirteen of those held could face up to 15 years in jail for creating "mass disturbances", local media reported.
The violence is in fact restricted to one small zone in central Kiev, close to the main protest encampment at Maidan (or Independence Square), with most of the rest of the city functioning normally, say correspondents.
Key opposition figures Arseniy Yatsenyuk and former boxing champion Vitali Klitschko have condemned the violence but seem unable to stop it, correspondents add.
Mr Klitschko has accused the government of paying thugs nicknamed "titushki" to delegitimise the protests through violence and create a pretext for the imposition of a state of emergency.
Mr Klitschko's spokeswoman wrote on Facebook that he, personally, caught, disarmed and interrogated two "titushki" during the night.
BBC spoke to several suspected "titushki" detained by the opposition activists.
One, an 11th-year student called Nikolai Ignatenko, said:
"We weren't told anything about what to do. We stood by the metro and waited. They gave us hammers - that's all".
Artyom Nemchenko, a college student, said:
"I wanted to earn some money, I found an offer on the internet. They were offering 220 hryvnia (£16; $26)."
He said some of the provocateurs "were instructed to stir up trouble: erect barricades, launch attacks".
A raft of anti-protest laws passed hastily by parliament last week was published in Holos Ukrainy, a parliamentary newspaper, on Tuesday, and are due to come into force on Wednesday, said reports.
They prescribe jail terms for anyone blockading public buildings, and ban the wearing of masks or helmets at demonstrations.
They also ban any unauthorised tents in public areas and make slandering government officials a crime.
In a statement on Monday evening, President Yanukovych said that "now, when peaceful actions are turning into mass unrest, accompanied by riots and arson attacks, the use of violence, I am convinced that such phenomena are a threat not only to Kiev but to the whole of Ukraine".
But talks mooted between President Yanukovych and opposition leaders failed to materialise; instead their deputies met on Monday.
Lesya Orobets, an MP for the Fatherland opposition party, said the talks "showed almost no result", and complained that the president's chief negotiator was implicated in an earlier violent crackdown on protesting students.
She called for a high-ranking foreign mediator to oversee the talks.
Source: BBC News