Paris attack: No 10 says UK to work closely with France
The UK will work closely with French authorities following the Paris terror attack, Downing Street has said.
The PM's spokesman said David Cameron was being regularly updated and would receive a full security briefing on Wednesday evening.
Mr Cameron condemned the "barbaric" shootings at the offices of Charlie Hebdo magazine, in which at least 12 people were killed.
The Queen has offered "sincere condolences" to victims and families.
Speaking at a press conference with German Chancellor Angela Merkel in Downing Street, Mr Cameron said the two leaders had been briefed by MI5 and MI6 on the attack.
The UK and German leaders spoke to French President Francois Hollande by phone and offered whatever assistance was needed.
Home Secretary Theresa May will chair a meeting of the emergency Cobra committee on Thursday.
Prime Minister's Questions on Wednesday opened with statements about the killings, with Mr Cameron and Labour leader Ed Miliband vowing to defend democracy and press freedom.
In the Commons, Mr Cameron said: "We stand squarely for free speech and democracy. These people will never be able to take us off those values."
Mr Miliband told MPs he felt "horror and outrage", adding: "We stand in solidarity with the people of France against this evil terrorist attack by people intent on attacking our democratic way of life and freedom of speech."
Deputy Prime Minister Nick Clegg described the killings as a "barbaric attack on freedom of speech".
"My thoughts are with the victims, their families and their colleagues," he said.
Speaking during a Commons debate on the Counter-Terrorism and Security Bill, Mrs May said the attack showed the threat in countries across the world was "grave and relentless".
"We need to keep our terrorism laws and capabilities under review and ensure that the police and intelligence agencies have powers to do their job and that is why this counter-terrorism and security bill is so important," she said.
London Mayor Boris Johnson tweeted: "Shocked and appalled by senseless attack at Charlie Hebdo - London stands with Paris and the people of France against this horrific scourge."
UKIP leader Nigel Farage said the attack was "truly horrific" and had "some very worrying implications for our civilisation - free speech, satire, all things that Western countries believe in and love and have enjoyed for centuries".
He said there was a "fifth column" within London and Paris and it should lead people to question multicultural policies.
Ian Hislop, editor of British satirical newspaper Private Eye, offered his condolences and said the victims "paid a very high price for exercising their comic liberty". He added: "Very little seems funny today."
Advice for British visitors to France on the Foreign Office website has been amended to read: "A number of people have been killed and injured. If you're in Paris or the Ile-de-France area, take extra care and follow the security advice issued by the French authorities."
"There is a high threat from terrorism. Attacks could be indiscriminate," the advice continues.