Vladimir Putin has signed laws completing Russia's annexation of Crimea and vowed to protect a bank that has been blacklisted by Washington.

The Russian president, who took part yesterday's ceremony at the Kremlin, signed the ­ratification of a treaty making the Ukrainian territory part of Russia as well as laws creating two new administrative districts, Crimea and the port city of Sevastopol, where Moscow keeps part of its Black Sea fleet.

Mr Putin said he would respond to financial sanctions against a leading bank and travel bans on officials imposed by Washington. He has already barred a number of White House officials and US politicians from travelling to Russia.

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However, Mr Putin has accepted a six-month fact-finding mission to help defuse the continuing controversy in Ukraine following the annexation of Crimea.

About 100 civilians from the Organisation for Security and Co-operation in Europe (OSCE) are to go into the country in an effort to build "peace, stability and ­security."

The OSCE works on consensus, and Russia's approval could signify a slight de-escalation of tensions. Pro-Russian forces last week stopped OSCE military observers from entering Crimea. That team was requested by Ukraine and its formation did not need Russian approval.

The Moscow stock market, which has seen shares plunge by $70 billion (£42bn) since the crisis began, fell sharply again after US President Barack Obama also threatened to target major sectors of the economy if Russia moved on areas of Ukraine beyond the Black Sea peninsula.

Washington is sceptical of Russian assurances that troop movements on the Ukraine border were no more than military exercises and the OSCE agreed to send monitors to Ukraine.

Visa and MasterCard have stopped processing payments for the St Petersburg-based Bank Rossiya. The institution is chaired by Yuri Kovalchuk, an associate of Mr Putin. It mainly serves energy businesses owned by state-run gas producer Gazprom. Mr Putin, who says Crimea exercised its right to self-determination in Sunday's disputed referendum, promised to transfer his wages there. "I personally don't have an account there, but I certainly will open one on Monday," he told Russia's Security Council.

Finance Minister Anton ­Siluanov said Russia might cancel its foreign borrowing for 2014 and raise less domestically if the cost of issuing debt rose.

European Union leaders imposed their own sanctions on 12 people, including Russian deputy prime minister Dmitry Rogozin and two aides to Mr Putin.

Shaken by the worst crisis since the Cold War, they also expressed their determination to reduce the EU's reliance on Russian energy, and signed a political deal with the Kiev leadership that took power after Moscow-backed ­President Viktor Yanukovich's overthrow last month.

Thousands of Russians marked the annexation with fireworks and celebrations in Simferopol, the capital of Crimea, where the population is about 58% ethnic Russian.

In Kiev, police detained the head of the Naftogaz state energy firm, Yevhen Bakulin, over allegations he embezzled $4bn (£2.4bn) during former Prime Minister Viktor Yanukovych's time in power.