President Barack Obama and British Prime Minister David Cameron say they will not allow terrorists to suppress free speech and free expression.
In joint opinion piece published in The Times of London, the two leaders promised to "defeat these barbaric killers and their distorted ideology." Obama and Cameron said the world would "not be cowed by extremists," whether they were "lone fanatics" or groups such as al-Qaida, the Islamic State or Boko Haram.
The article came after last week's deadly terrorist attack on the offices of the French satirical magazine Charlie Hebdo.
In their opinion piece, the leaders also vowed to maintain diplomatic pressure on Russia over its actions in Ukraine.
Obama held a working dinner with Cameron at the presidential residence in Washington on Thursday. The White House said they would meet Friday to discuss a range of issues, including terrorism, Ebola and Russia's actions in Ukraine.