German Chancellor Angela Merkel will address parliament and have tea with the Queen in a high-profile visit to London today where she is expected to indicate her support for Britain staying in the European Union.
Merkel's support is seen as crucial to David Cameron's aims to reform the country's relationship with the EU.
The Prime Minister has promised to renegotiate the UK's membership and hold an in-out referendum in 2017 if the Conservatives win the general election next year.
The German Chancellor will also hold meetings with Ed Miliband and Nick Clegg.
Russia's President Putin and the German Chancellor Merkel held a phone conversation to discuss the situation in Ukraine, the Kremlin has said.
"They underscored their joint interest in a stable Ukraine - both in economic and political terms," Merkel's spokesman Steffen Seibert said in a statement, adding they had agreed to stay in close contact.
David Cameron has phoned German Chancellor Angela Merkel to discuss the "spiralling violence" in Ukraine, a Number 10 spokesperson said.
The Prime Minister called Chancellor Merkel earlier this afternoon to discuss the appalling situation in Ukraine.
They are both extremely concerned by the spiralling violence. They agreed that the immediate priority must be to stop the violence and that President Yanukovych has a particular responsibility to help de-escalate the situation by pulling back government forces.
The Prime Minister plans to speak to more leaders in the next 24 hours and Ukraine will feature on the agenda of the PM’s bilateral with Dutch Prime Minister Mark Rutte tomorrow afternoon.
Angela Merkel must take it easy for three weeks and work from home where possible after a skiing accident, said her spokesman Steffen Seibert.
The accident happened last week when the Chancellor fell while skiing over the Christmas vacation.
"The chancellor is of course able to work and is in full communication," said Seibert. He added that Merkel's accident occurred "at low speed" but he declined to give further details. The chancellor has postponed a visit to Warsaw scheduled for Wednesday this week, Seibert added.
But she will lead a cabinet meeting on Wednesday which will be the first gathering of all the ministers in the new "grand coalition" government of her conservatives and the centre-left Social Democrats (SPD), which was formalised last month.
AFP's Berlin correspondent Deborah Cole says chancellor Angela Merkel has cancelled nearly all meetings for three weeks following a skiing accident.
A journalist from German broadcaster Deutsche Welle says Angela Merkel has broken her pelvis in a skiiing accident.
GroKo is short for "grosse Koalition", a grand coaliton of the two large camps from centre-left and centre-right within German politics.
German Chancellor Angela Merkel has been injured while skiing and has cancelled several meetings, a spokesman told news agency AFP.
The United Nations has received assurances from the US Government that its communications networks "are not and will not be monitored" by American intelligence agencies, it said.
But chief UN spokesman Martin Nesirky would not comment on whether the world body had been monitored in the past, as reported recently by the German magazine Der Spiegel.
Mr Nesirky said the UN had been in contact with Washington about the reports that surfaced two months ago and has received a guarantee from the US of no current or future eavesdropping.
The National Security Agency, responsible for electronic eavesdropping for the US, has been forced to deny reports that it spied on the Vatican, and released a statement saying an Italian media report that it had done so was "not true."
In a statement, the NSA said:
"TheNational Security Agency does not target the Vatican. Assertions that NSA hastargeted the Vatican, published in Italy's Panorama magazine, are not true."
The Holy See said it had no knowledge of any such activity.
Russian President Vladimir Putin has been voted the world's most powerful leader, pushing US counterpart Barack Obama to second place, according to Forbes magazine.
In third place is Xi Jinping, the general secretary of the Communist Party of China, while German Chancellor Angela Merkel comes third and UK Prime Minister David Cameron is some way behind in 11th.
Women make up only 12 per cent of people on the 'most powerful' list. Among them are Brazilian leader Dilma Rousseff (no.20) and the de facto head of India, Sonia Ghandi (no. 21).
Billionaires Warren Buffett (no. 13) and Michael Bloomberg (no. 29) warranted special mention because of their philanthropic work, said Forbes.
Newcomers to the list include Pope Francis (no. 4) and Samsung Chairman Lee Kun-Hee (no. 41).
The list of global power-brokers is voted for by Forbes editors, who pick 72 leaders - one for every 100 million people on Earth - based on influence and wealth.