World leaders express support for UK after London attack

World leaders denounced on Wednesday the attack near the British Parliament in London, after an attacker ploughed his car into pedestrians and then stabbed a policeman, in what authorities called a "marauding terrorist attack".

Five people, including the assailant, were killed in the incident.

German Chancellor Angela Merkel expressed shock at the attack, saying her thoughts were with the British people and everyone in the British capital.

"Although the background to these incidents still needs to be exactly clarified, I confirm on behalf of Germany and its citizens that we stand firmly and resolutely by Britain's side when it comes to fighting any kind of terrorism," Merkel said in an emailed statement.

Late on Wednesday, UK police said "Islamist-related terrorism is our assumption behind London attack."

US President Donald Trump offered British Prime Minister Theresa May Washington's full cooperation and support in responding to the incident, the White House said in a statement.

Trump also praised the "effective response" of UK security forces.

New York police ramped up security at British sites across the city following the attack.

Heavily armed officers and explosives-detecting dogs were deployed to locations like the British Consulate and the British Mission to the United Nations in Manhattan, senior New York Police Department officials said at a news conference.

Meanwhile, French President Francois Hollande expressed solidarity with Britain after the attack, in which three French school children were injured.

"We are all concerned with terrorism," Hollande said at a news conference. "France, which has been struck so hard lately, knows what the British people are suffering today."

Hollande called for international cooperation to "answer these attacks".

Australian Prime Minister Malcolm Turnbull said security will be beefed up around the country's parliament on Thursday.

"We work very, very closely with our allies, including the United Kingdom and the United States and many other partners around the world," Turnbull told reporters. "But we must be clear-eyed about the risk. It is real and that is why terror threat level is set at probable."

The Gulf Cooperation Council also denounced the incident.

“The Cooperation Council strongly condemns the attack and considers it a gruesome crime that contradicts all human and ethical values,” GCC secretary general Abdullatif bin Rashid Al Zayani said, according to official Saudi media agency SPA.

Palestinian Authority president Mahmoud Abbas also offered his condolences to May, condemning the attack as an act of "terror", and saying Palestinians stand with the British people in these difficult times.

Qatar stressed its rejection of violence "in all its forms" and its support for the UK government "in all the measures it takes to maintain the country's security."

Turkish President Recep Tayyip Erdogan emphasised that "Turkey feels and shares deeply in the United Kingdom's pain" and that it stood in "solidarity" with Britain "in the fight against terrorism".

Erdogan had earlier warned Europeans in a speech on Wednesday that "no European, no Westerner will be able to take steps on the street safely and peacefully," as a crisis between Ankara and the EU showed no signs of abating.

Turkish Prime Minister Binali Yildirim called terrorism "a global catastrophe" on Turkish television, adding: "All countries should come together on the terror issue and fight together against" it.

Russian Foreign Ministry spokeswoman Maria Zakharova expressed condolences to the people of Britain and urged collective action to defeat the "evil" of terrorism.

"It is necessary to focus efforts not on seeking imaginary threats, not on increasing the budget to counter nonexistent challenges, it is necessary to concentrate and combine the efforts of the entire international community to counter real threats," she told Rossiya 24 TV channel.

Dutch Prime Minister Mark Rutte also expressed support for the UK. "The British can count on our support. We are monitoring the situation closely and are in contact with the British authorities,” he wrote on Facebook.