The case for tougher sanctions against Russia gets stronger every day Moscow fails to match its welcome for the Ukraine government's peace plan with concrete action, British Foreign Secretary William Hague said Wednesday.

The shooting down of a Ukrainian helicopter, killing all nine on board, by pro-Russian rebels Tuesday, was hard to reconcile with President Vladimir Putin's backing of the plan, Hague said.

Russia on Wednesday said it hoped Kiev and the international community will heed the "positive signals" it was sending over the Ukraine crisis after President Vladimir Putin moved to scrap the option to invade. 

"We are counting on the positive signals that the Russian president is now sending being heard across the world and, above all, in Ukraine," Deputy Foreign Minister Grigory Karasin told Russian news agencies. 

Nine Ukrainian servicemen died on Tuesday when pro-Russian insurgents shot down an army helicopter in the separatist east, which prompted Ukraine's new Western-backed president to warn that he may revoke his one-week unilateral ceasefire to allow government forces to retaliate for the incident.

"There were nine people on board the helicopter. According to preliminary information... everyone on board died," Ukrainian defense spokesman Vladyslav Seleznyov wrote in a Facebook post.

Russian President Vladimir Putin on Tuesday urged Kiev to extend the shaky truce with insurgents in eastern Ukraine and launch talks despite them shooting down a helicopter with nine on board.

The Russian strongman said he had asked senators to rescind a resolution allowing him to invade Ukraine in order to encourage a "peace process" but vouched at the same time to always protect the interests of Russians in the neighboring country.

Russian security officials in the country's second city of Saint Petersburg have detained alleged members of banned Islamist group Hizb ut-Tahrir, Russia's FSB security agency said Tuesday.

Hizb ut-Tahrir (Party of Liberation) seeks to re-establish a caliphate -- a pan-Islamic state based on Islamic rule harking to the medieval era -- and has been banned in Russia since 2003.

Ukraine's new Western-backed president faced pressure on Tuesday to negotiate with top rebel commanders after a surprise turnabout in which the insurgents agreed to a truce and talks on ending their pro-Russian uprising.

The prominent head of the self-declared Donetsk People's Republic on Monday unexpectedly reversed his firm rejection of President Petro Poroshenko's peace overtures by agreeing to a ceasefire that would last until Friday morning.

Russia on Monday hailed the "successful" completion of an international mission to ship chemical agents out of Syria, under a U.S.-Russia brokered agreement that helped avert the threat of Western air strikes.

"Russia greets the successful end of a large-scale and unprecedented international operation to ship all components of chemical weapons and their precursors out of Syria with deep satisfaction," the foreign ministry said in a statement.

European Union foreign ministers urged Russia on Monday to back the Ukraine government's peace plan or face tougher sanctions.

The 28 EU ministers were also seeking a policy response on Iraq and examining fallout from the Syrian conflict that is destabilizing the Middle East, driving a refugee exodus washing up on EU shores.

Iran is moving to finalize plans with Russia to build at least two more nuclear power plants on the Islamic republic's southern Gulf shores, media reports said on Monday.

The announcement came as Russia's Rosatom deputy chief Nikolai Spassky arrived in Tehran for a two-day visit during which he will meet senior nuclear officials.

Ukraine's pro-Russian insurgents agreed for the first time on Monday to a temporary ceasefire and talks with the new Western-backed president on ending 10 weeks of fighting that have threatened the very survival of the ex-Soviet state.

The surprise announcement from the head of the self-proclaimed Donetsk People's Republic came a day after Russian President Vladimir Putin publicly threw his weight behind Kiev's peace overtures and urged the separatists to halt fire.