He doesn't bluster and he doesn't strut and President Barack Obama certainly isn't panicking, though he admits it feels like the world is falling apart.

But Obama's cool-in-a-crisis style and disdain for the impulsive use of military force is fueling criticism of his leadership, as crises stagger the Middle East and Ukraine.

The Swedish military said Saturday it had increased intelligence gathering and called in extra staff to its headquarters over the crisis in Ukraine, as the prime minister compared Russia's current behaviour with the Cold War.

"We have raised the level of readiness at headquarters in particular areas, for example in intelligence gathering," armed forces spokesman Niklas Englund told Agence France Presse.

Pro-Russian rebels in east Ukraine warned on Saturday that they will launch a fresh offensive against government troops, days after seizing swathes of territory.

Kiev and the West accuse Moscow of sending regular army soldiers across the border to spearhead the lightning counter-attack that saw the tide turn after months of Ukrainian advances.

The so-called Contact Group on Ukraine will meet Monday in Minsk, Belarussian officials said, as the Kremlin emphasized the importance of having separatists participate.

The Belarussian foreign ministry said representatives of Kiev, Moscow and the OSCE would attend the talks but did not provide details.

Lithuanian President Dalia Grybauskaite on Saturday warned Russia was practically at war with Europe and urged tougher sanctions against Moscow.

"Russia is at war against Ukraine and that is against a country which wants to be part of Europe. Russia is practically in war against Europe," said Grybauskaite, one of Moscow's harshest critics, as she arrived for an EU summit.

The European Union geared up a fresh wave of sanctions against Russia on Saturday with warnings that the escalating conflict in Ukraine was putting all of Europe at risk of war.

Fears of a wider confrontation spiraled after allegations that Russia has sent troops and weapons across the border to help a bloody new counter-offensive by pro-Kremlin rebels.

A Ukrainian cargo plane crashed in the Sahara desert early on Saturday, killing all seven people on board, Algeria's transport ministry said.

The Antonov 12, which had come from Glasgow in Scotland and was bound for Equatorial Guinea, came down near Tamanrasset airport at around 2:40 am (0140 GMT), a ministry statement said.

A prominent Russian politician who attended the secret funerals of soldiers apparently killed in Ukraine was attacked and hospitalised with a head injury, his party said on Saturday. 

A senior military official said Saturday that Russia wants a "humanitarian bridge" to ferry multiple aid shipments into war-torn areas of eastern Ukraine.

Russian authorities, social organisations and businesses "are thinking of organising not one humanitarian convoy, which we have already sent, but a second, third, tenth," Deputy Defense Minister Anatoly Antonov told the state RIA-Novosti news agency in an interview.

A Ukrainian fighter jet has been shot down by a Russian anti-aircraft system in the east of the country, where Kiev is fighting pro-Moscow rebels, Ukraine's military said on Saturday.