Donald Trump, the President-elect of United States, condemned the assassination of Russia's ambassador to Turkey, calling the gunman a "radical Islamic terrorist."
"Today we offer our condolences to the family and loved ones of Russian Ambassador to Turkey Andrei Karlov, who was assassinated by a radical Islamic terrorist," Trump said in a statement.
"The murder of an ambassador is a violation of all rules of civilized order and must be universally condemned.
Condemning the Berlin attack, he said: "Our hearts and prayers are with the loved ones of the victims of today's horrifying terror attack in Berlin. Innocent civilians were murdered in the streets as they prepared to celebrate the Christmas holiday."
A lorry ploughed into a busy Christmas market in central Berlin yesterday, killing at least nine people and hurting 50 more in what police said was a possible terror attack.
"ISIS and other Islamist terrorists continually slaughter Christians in their communities and places of worship as part of their global jihad. These terrorists and their regional and worldwide networks must be eradicated from the face of the earth, a mission we will carry out with all freedom-loving partners," Trump said.
In a tweet, Trump said, in view of the terrorist attack yesterday the civilised world must change its thinking.
"Today there were terror attacks in Turkey, Switzerland and Germany - and it is only getting worse. The civilised world must change thinking," he wrote.
President Barack Obama, who is on a vacation in Hawaii, was briefed about the assassination by his national security aide, the White House said.
"This morning the President was briefed by his National Security Team on the assassination of the Russian Ambassador to Turkey in Ankara today. The President directed his team to provide updates as warranted," White House Deputy Press Secretary Eric Schultz said.
Earlier in a statement, US Secretary of State John Kerry condemned the assassination of Russian Ambassador and offered all American help in the investigation into the tragic incident.
"The US condemns the assassination today in Ankara of Russian Ambassador Andrey Karlov. Our thoughts and prayers are with his loved ones, the Russian people, and with the other victims who were injured in this shooting," Kerry said.
"We stand ready to offer assistance to Russia and Turkey as they investigate this despicable attack, which was also an assault on the right of all diplomats to safely and securely advance and represent their nations around the world," he added.
The Senate Intelligence Committee Vice Chairman Dianne Feinstein said the "horrifying assassination" of Russian Ambassador Andrei Karlov is beyond the pale.
"This was an attack not just on a Russian diplomat but all nations that respect the rule of law and the importance of diplomacy," she said.
"Such an attack on a member of the diplomatic corps is wholly unacceptable. Diplomacy is a noble calling that can bring forward the hope of stability and peace; violence only will bring more violence, more loss and more suffering," said Senator Ben Cardin, Ranking Member of the Senate Foreign Relations Committee.
"The United States stands firmly with the German people during this time of national sadness, and we offer any support they may require," State Department Spokesman John Kirby said.