BRUSSELS  - US President Barack Obama announced a new round of punitive measures for Moscow’s annexation of Crimea on Thursday as Europe’s leaders also readied to hit back at Russia with fresh sanctions.

But in Moscow, where the lower house of parliament rubber-stamped the absorption of the rebel peninsula, Russia issued its own list of sanctions against US officials.

Obama, who threatened to target the broader Russian economy if Moscow escalates its actions against Ukraine, said: “Russia must know that further escalation will only isolate it further from the international community.”

The latest US measures in the worst East-West crisis since the Cold War target a new list of 20 lawmakers and senior government officials in addition to 11 people already sanctioned by Washington.

In Brussels, where the 28-nation European Union was gathering for its second summit on Ukraine in less than two weeks, French President Francois Hollande said: “Borders cannot be redrawn and a region allowed to pass from one nation to another without a response.”

Hollande said the bloc’s leaders would announce fresh sanctions at the two-day meeting “against a certain number of figures” and would cancel an EU-Russia summit planned for June.

But EU nations for now remain divided on ramping up their response with biting economic sanctions, hoping that diplomacy and dialogue can provide a way out.

“We will make clear that we are ready in case of further escalation to introduce economic sanctions,” said German Chancellor Angela Merkel, whose country is Russia’s leading EU trading partner.

Urging the bloc “to speak with a clear and united voice”, Britain’s Prime Minister David Cameron said all were agreed on helping build a strong and democratic Ukraine. Kiev’s interim premier Arseniy Yatsenyuk will be in Brussels to sign the political parts Friday of a broad EU Association Agreement whose rejection in November by Ukraine’s pro-Kremlin president Viktor Yanukovych sparked the protests that led to his fall.

Russian President Vladimir Putin found himself on the diplomatic defensive in Moscow when United Nations Secretary-General Ban Ki-moon told him: “I cannot but to tell you that I am deeply concerned.” Ban called for the deployment to Ukraine of rights monitors from the UN and the Organisation for Security and Co-operation in Europe (OSCE) and for an “honest and constructive dialogue” between Moscow and Kiev. But world anger has done little to halt the unchallenged Russian military advances that prompted Kiev’s new Western-backed government to acknowledge preparing a Crimean evacuation plan for thousands of Ukrainian soldiers and their families.

Tensions eased somewhat in the region when acting president Oleksandr Turchynov announced the release Thursday by Crimean militias of Ukranian navy chief Sergiy Gayduk. Turchynov hd threatened the Crimean authorities with “an adequate response ... of a technical and technological nature” unless they immediately freed Gayduk and several others who were captured during the storming of Ukraine’s naval headquarters in the port of Sevastopol on Wednesday.

The march by Moscow‘s troops and pro-Kremlin militias across the mostly Russian-speaking region roughly the size of Belgium has been unhalting since the day Putin won parliamentary approval to use force against his ex-Soviet neighbour following the February 22 fall of Yanukovych. Kiev’s untested leaders now fear that Putin has set his sights on Russified southeastern swathes of Ukraine as part of his self-declared campaign to “protect” compatriots.  “There are indications that Russia is braced to unleash a full-blown intervention on Ukraine’s east and south,” Ukraine UN ambassador Yurii Klymenko told reporters in Geneva.

Russia’s Federal Customs Service stepped up the pressure on Thursday by announcing tougher and more time-consuming inspections of goods entering the country from Ukraine that it said were aimed at intercepting possible illicit shipments of arms.

Ukraine has announced plans to withdraw from the Moscow-led Commonwealth of Independent States (CIS) alliance that replaced the Soviet Union and to slap visas on Russians who want to enter the country.

EU leaders have already suspended talks on easing visa requirement for Russian travellers into Europe - an issue that Moscow has lobbied for for years - and slapped travel bans and asset freezes on 21 Russians and Ukrainians considered culpable for the Crimean swoop.

But the measures covered a much lower rank of officials than the punitive steps announced by Washington against 11 Russians and Ukrainians.

Those included Yanukovych and some key Putin allies. Germany appeared set to pursue a more forceful push against Russia by on Wednesday announcing the suspension of a major arms deal with Moscow.

But France resisted pressure to make a similar gesture, saying on Thursday that it was putting off a decision on whether to shelve its disputed sale of a second state-of-the-art Mistral warship to Russia until October - the expected delivery date of the first vessel.

Russia’s Deputy Foreign Minister Sergei Ryabkov earlier warned that Moscow was preparing an entire series of “asymmetrical measures” should the US hit his country with more severe measures.

Ryabkov said these covered “a number of areas of dialogue... that are important to the Americans” and hinted that Russia could “raise the stakes” in the ongoing Iranian nuclear talks.