Concerns are growing that a shaky, three-month-old cease-fire in Ukraine between government forces and Russian-backed rebels could in the coming weeks break down completely into all-out fighting and block the path for implementing an agreed upon peace deal.
The latest cease-fire was agreed to in Minsk in February as the first step in a wider political settlement touted as the last, best hope for a solution to the Ukraine crisis. Previous attempts at a deal were less comprehensive and fell apart as clashes spiked sporadically and territory was lost.
Despite relative calm this week, the Organization for Security and Cooperation in Europe's Special Monitoring Mission on Ukraine (OSCE SMM) noted an increase in violations this month, including movement of heavy weapons.
Alexander Hug, the OSCE's deputy chief monitor, told journalists in Kyiv Thursday the conflict was most pronounced around the rebel-controlled Donetsk airport and Shyrokyne, a coastal town on the Sea of Azov about halfway between the Russian border and the Ukrainian government-controlled port city of Mariupol.
Hug said talks this week in Minsk gave him a sense the sides are not far apart on what needs to be done to de-escalate in Shyrokyne and are discussing a pullback to reduce tensions. But, he added, “Worryingly, the geographical scope of the conflict seems to be spreading to residential areas of Horlivka, just north of Debaltseve.”
He said the two sides were, at best, "only partially complying" with the Minsk agreement obligation on withdrawing heavy weapons.
The OSCE's SMM reported the presence and movement of tanks, troop carriers, artillery and rocket launchers – some in and out of facilities where they were supposed to be stored.
OSCE unmanned aerial vehicles recently spotted an advanced surface-to-air missile system in rebel-controlled territory in Oktyabr, 25 kilometers from Mariupol.
Kyiv fears summer offensive
For months, Kyiv has raised fears that the Russian-backed rebels aim to retake Mariupol in order to gain access to the sea and possibly push farther west to form a land bridge between Russia and Crimea, the Black Sea peninsula the Kremlin annexed last year.
The rebels briefly took control of Mariupol a year ago before Ukrainian forces pushed them out of the city.
Loyalties in Mariupol are divided and most analysts believe the Russian-backed rebels, if ordered, could take the port.
Ukrainian authorities said since the cease-fire was signed, at least 83 of their troops have been killed, including eight since Monday.
In an interview Wednesday with the BBC, Ukrainian President Petro Poroshenko said he believes the Russian-backed rebels are preparing a summer offensive.
Dmitri Trenin, director of the Carnegie Moscow Center, said the rebels will not make a move without the approval of Russian President Vladimir Putin.
He argued Putin's recent remarks praising Western allies during World War Two indicate conciliatory, rather than military action in Ukraine, which the Kremlin sees as a fight for influence with the West.
"To me, what it suggests is that the mood of the Kremlin is geared toward some kind of an accommodation,” Trenin said. “Maybe partial, maybe imperfect, maybe temporary even, but accommodation – not a new war effort."
Vows to take territory
At a press conference in the rebel-held city of Donetsk last week, Aleksandr Zakharchenko, the self-declared leader of the Donetsk People's Republic, repeated aims to eventually take all territory in southeast Ukraine, known as the Donbas.
"I consider and will consider the territory of the Donetsk region, which is currently under Kyiv authorities, illegally occupied and a subject to liberation,” Zakharchenko said. “By what means it will happen – time will tell."
He named the specific towns they would "liberate" as Slovyansk, Krasnoarmeisk and Mariupol.
On Wednesday, Eduard Basurin, another rebel spokesman, denied any planned offensive.
Russian and rebel leaders said Ukrainian authorities are the ones who appear to be preparing to fight and cite recent comments from Poroshenko about taking back the Donetsk airport.
U.S. Secretary of State John Kerry, this month, on his first trip to Russia since the Ukrainian crisis, issued a rare warning to Poroshenko, urging him not to take any offensive measures against the rebels that could spark renewed conflict.
Poroshenko responded to Kerry's concerns in the BBC interview, saying Ukraine should be ready to defend itself but also to "not give them any tiny chance for provocation."
Both Kerry and German Chancellor Angela Merkel have held separate meetings with Putin in Russia and all sides stressed the importance of sticking to the Minsk agreement.
Crimea for Donbas
Russian Foreign Minister Sergei Lavrov said Kerry did not raise the issue of Crimea's status during the meetings in Sochi with him or Putin.
While observers point out Western politicians have been raising the issue less vocally in recent weeks, it seems to reflect a change in tone, not policy.
The United States, European Union and other Western allies maintain that Crimea is part of Ukraine, under Russian occupation and must be returned to Kyiv.
Chancellor Merkel called Russia's seizing of the Black Sea peninsula an illegal, criminal act.
Trenin, of the Carnegie Moscow Center, said the Kremlin is formulating a deal that seeks international recognition of Crimea as part of Russia.
"I heard Minister Lavrov many months ago describing Russia’s formula for the resolution of the Ukraine crisis," he said. "And, it was very simple: Crimea is Russian – Donbas is Ukraine. Well, it needs to be elaborated clearly; but, that’s the formula that the Russians are coming up with."
Russia 'sticking' to its guns?
Pavel Felgenhauer, a defense analyst and columnist with Novaya Gazeta newspaper in Moscow, argued there are few signs pointing to a de-escalation of the military confrontation in Donbas.
"If you want a frozen conflict," Felgenhauer said, "you have to try and rebuild the basis of peaceful existence, at least to some extent."
Instead of that, he argued, "all the effort is going into re-arming and reorganizing the rebel forces and proxy forces for a new offensive, which means it is inevitable."
Many political analysts said they believe the Kremlin is supporting the rebels to maintain leverage over the Western-leaning government in Kyiv and prevent it from joining NATO, the Western military alliance.
NATO chief Jens Stoltenberg met Tuesday with Russian Foreign Minister Sergei Lavrov and expressed concern about the large number of Russian military exercises carried out at short notice. He also urged that Moscow withdraw military support for rebels.
Ukrainian authorities this week announced it captured two Russian troops in rebel territory sent by the Kremlin.
Moscow denied the men were active soldiers, sticking to its line that only volunteers are helping the rebels.
When 10 active duty Russian paratroopers were captured in Ukraine last August, Russian authorities said the paratroopers got lost and accidentally crossed the border.
The OSCE SMM met two of the captured Russians Tuesday at a hospital in Kyiv.
The men admitted to the international monitors they were active duty military on a reconnaissance mission. One of them said he received orders to go to Ukraine while both said they had been to Ukraine on missions before.
Trenin said the buildup of evidence pointing to Russia's covert military support for the rebels is slowly being recognized by the Russian public.
"I think that they guessed that Russia is helping militarily in various ways," he said. "They may not know how many soldiers or servicemen have been involved in all that, but I think that, basically, they think that Russia is involved and that that’s the right thing – to be involved."
Trenin said Russian propaganda has most Russians believing the conflict in Ukraine is a fight between Russia and the United States rather than Russia and Ukraine.
The United Nations said more than 6,200 people have been killed in eastern Ukraine since Russian-backed rebels seized government offices more than a year ago and declared the area republics.