Russia has warned that it will hit back against the West if tougher sanctions are imposed over the conflict in Ukraine - as a shaky ceasefire in the region holds.
Dmitry Medvedev blamed countries backing Ukraine for damaging the Russian economy with "stupid" sanctions and suggested Moscow could retaliate by stopping flights over Russian airspace.
The Russian prime minister told the Vedomosti newspaper Russia may have been too patient in responding to sanctions imposed so far by the United States and European Union over the Kremlin's role in Ukraine - and warned the mistake would not be repeated.
He said: "If there are sanctions related to the energy sector, or further restrictions on Russia's financial sector, we will have to respond asymmetrically.
"If Western carriers have to bypass our airspace, this could drive many struggling airlines into bankruptcy. This is not the way to go.
"We just hope our partners realise this at some point."
It comes as Russian President Vladimir Putin spoke with his Ukrainian counterpart Petro Poroshenko about a peaceful resolution to the crisis.
The conversation allowed the leaders to discuss "steps that will facilitate a peaceful resolution to the situation", according to a Kremlin statement.
A new package of EU-agreed sanctions, which would hit oil and gas giants Rosneft and Gazprom, is due to come into force on Monday but could be suspended if Russia is judged to be working towards a resolution of the Ukraine conflict.
A ceasefire agreed on Friday by envoys from Ukraine, the leadership of pro-Russian separatists fighting Kiev government forces, Russia and Europe's OSCE security watchdog has been tested by fighting in eastern Ukraine.
OSCE chair Thomas Greminger said on Monday that the truce was holding, although "it is still shaky".
The ceasefire is part of a peace plan to end the five-month conflict, which the United Nations' human rights envoy says has now killed more than 3,000 people.
Speaking on a visit to Mariupol, Mr Poroshenko revealed separatists have so far handed over around 1,200 prisoners of war under the terms of the truce agreement.
He said he had reinforced the frontline city with tanks, rocket launchers and aerial defences as he vowed: "We will not give up this land to anybody".
Updating MPs on last week's Nato summit in the House of Commons, David Cameron said he had agreed with Mr Poroshenko and the leaders of France, Germany, Italy and the US that a "proper peace plan" that respects Ukraine's territorial integrity was needed.
Ukrainian forces said they had come under sporadic fire overnight from pro-Russian separatists in eastern Ukraine and listed rebel violations of the agreement in five sites, while the separatists accused government forces of preparing to storm a town near rebel-held Donetsk, the region's industrial hub.
There were no reports of any overnight casualties.
Both the rebels and the Ukrainian military insist they are strictly observing the ceasefire and blame their opponents for any violations.
One woman was killed after shelling resumed near Mariupol on Saturday, while the area around Donetsk airport was hit by blasts on Sunday.
Before the ceasefire was agreed in Minsk, Russian-backed separatists had been advancing on Donetsk airport and Mariupol - a key city between Russia and Crimea, which Moscow annexed in March.
The Ukraine crisis could provide a tense backdrop to talks on Thursday between Russia and the US over a 1987 arms treaty agreement - which a Russian general suggested pulling out of earlier this year.