Ukraine said pro-Russian rebels targeted Mariupol, a frontline city in the east of the country, after President Petro Poroshenko announced his visit, further straining a four-day cease-fire.

Road blocks near the port city on the Sea of Azov came under fire from militants today, presidential spokesman Svyatoslav Tsegolko said on Twitter. Shelling and small-arms fire continued during the past 24 hours across the war-torn regions of Luhansk and Donetsk, said Andriy Lysenko, a spokesman for Ukraine’s National Security and Defense Council.

“I am not optimistic at all -- I have not been optimistic from the beginning,” Didier Burkhalter, chairman of the Organization for Security and Co-operation in Europe, which helped mediate and is monitoring the cease-fire, said at a news conference in Geneva. Even so, “we want to give it a chance.”

Poroshenko is visiting Mariupol against the backdrop of the uneasy stalemate between separatists and government forces, which have faced off in a conflict that the United Nations estimates has claimed at least 3,000 lives since mid-April. Both the authorities in Kiev and the rebels have been reporting casualties and violations of the truce that started at 6 p.m. local time on Sept. 5.

EU Sanctions

European Union governments approved further sanctions against Russia over its encroachment in Ukraine, Finnish Prime Minister Alexander Stubb told reporters in Helsinki today. The cease-fire isn’t yet holding, Stubb said, adding that’s he’s worried about a possible retaliation by the government in Moscow for the latest round of penalties. Russia denies involvement in the conflict.

“The move will doubtless entail immediate retaliatory action on the EU by Russia,” BNP Paribas SA analysts including Yevgeniy Orudzhev said in an e-mailed note to clients. “The sanctions are likely to exacerbate tensions between the EU and Russia, despite the cease-fire that has been observed in eastern Ukraine.”

Prime Minister Dmitry Medvedev said Russia may respond with “asymmetric” measures, Vedomosti newspaper reported. Last month, President Vladimir Putin banned some food imports from the U.S. and its allies to strike back for previous sanctions.

The EU would review its sanctions against Russia should the cease-fire hold, European Commission President Herman Van Rompuy said yesterday on VRT television.

Ruble, Bonds

The ruble weakened for the first time in four days and government bonds fell. The currency lost 0.4 percent to 41.9869 against the central bank’s target basket of dollars and euros as of 7:17 p.m. in Moscow, following a 2.2 percent gain in the previous three days. The Micex Index ended a four-day rally, with banks and energy companies leading the declines. The yield on 10-year local-currency bonds rose three basis points to 9.54 percent.

The ruble has retreated 11 percent against the dollar this year, the most among 24 developing peers tracked by Bloomberg after the Argentine peso.

Ukraine, which has accused Russia of deploying thousands of troops and using tanks and artillery to roll back the government’s offensive last month, has pressed for military assistance from the U.S. and Europe. Poroshenko said today that some North Atlantic Treaty Organization members have agreed to supply his government with modern weapons.

‘Comical’ Denials

While NATO isn’t sending weapons to Ukraine, its members can provide military assistance, said Alexander Vershbow, the alliance’s deputy secretary general.

To track Russia’s role in the conflict, NATO is relying on intelligence and evidence gleaned from satellites and media reports that corroborate its military presence in Ukraine, Vershbow said, adding that Russian denials are “comical.”

“Russia is not prepared to respect the sovereignty of its neighbors and their freedom to choose their international orientation,” Vershbow told reporters today by video link from NATO’s headquarters in Brussels. “And that’s the root of the conflict with Ukraine.”

The crisis in eastern Ukraine has reignited tensions between Russia and its Cold War adversaries. Ukraine’s failure to achieve a military victory over pro-Russian rebels means the country can’t remain a “unitary state” even if it maintains territorial integrity, a senior Russian lawmaker said.

‘Unitary State’

“It’s hard to imagine that Ukraine will be able to preserve itself as a unitary state after such a bloody conflict,” Alexei Pushkov, head of the foreign affairs committee in the lower house of parliament, said in an interview in Moscow, referring to a model of government based on the supremacy of central authority.

Separatists today said they have the right to resume fighting if Ukraine’s military uses weapons against them, according to a joint statement issued by the self-proclaimed Donetsk and Luhansk republics.

The conflict has pivoted to negotiations over the political future of the mainly Russian-speaking regions on Ukraine’s eastern frontier, where most of the fighting has raged. Rebel representatives said the cease-fire doesn’t change their goal of independence, which Poroshenko has ruled out, telling the BBC that he doesn’t intend to withdraw troops completely.

Speaking during a meeting with soldiers in Mariupol today, Poroshenko said artillery, tanks and other units were redeployed around the port city, which came under threat less than two weeks ago as rebel forces mounted a counteroffensive.

No Surrender

“Mariupol is Ukraine,” Poroshenko said on Twitter. “We will not surrender this land to anyone.”

The cease-fire pact contains 12 points, including prisoner swaps, pulling back the army and creating a buffer zone on the Russian-Ukrainian border, according to a document posted yesterday on the OSCE website. It also contains political concessions from the authorities in Kiev on temporary self- government in some areas of the Donetsk and Luhansk regions, as well as local elections and an amnesty.

While Ukraine’s National Security and Defense Council said yesterday that there’s no talk of ending the truce, explosions continued in the combat zone’s biggest city, Donetsk. The city council of Donetsk said on its website that residents heard shelling in many districts at about 5:30 p.m. local time today.

The Ukrainian Defense Ministry said today the rebels violated the cease-fire five times overnight. One soldier has died since the truce began, according to Poroshenko. The separatists said yesterday Ukrainian troops killed one militant in the village of Makiyivka and several more in another town.

Cease-fire Wobbles

The deaths were the first since the warring factions agreed to a cease-fire in the wake of a counteroffensive unleashed last month by the insurgents. Poroshenko and Putin spoke Sept. 6 by phone on the progress of the truce, agreeing that the Organization for Security and Cooperation in Europe should monitor it, according to the Ukrainian leader’s website. The next talks on the conflict may take place in a week.

“There’s no doubt the shelling creates the risk of the cease-fire breaking down,” Volodymyr Fesenko, a political analyst at the Penta research institute in Kiev, said yesterday by phone. “But if it’s just local shelling, rather than intensive military action, I think the truce will hold.”

De-Escalation Signs?

Some signs of de-escalation are emerging, with Lysenko saying that rebels released 20 prisoners and government forces sustaining no casualties during the past day. Poroshenko said today that 863 Ukrainians are still held by the separatists. Ukraine has seen no Russian troop movements over the border in the last 24 hours, even as forces were redeploying near the frontier in northern Crimea, the Black Sea peninsula annexed by Putin in March, Lysenko said.

Ukraine ordered some troops to retreat to new positions, according to Lysenko. He said Ukrainian forces have been adhering to the cease-fire and shooting only during life- threatening situations.

Even so, on his visit to Mariupol today, Poroshenko told his country to show resolve and brace for more adversity.