U.S. Secretary of State Tillerson condemns U.K. Parliament attack

Following the attack on the U.K. Parliament on Wednesday, U.S. Secretary of State Rex Tillerson has expressed condolence to the victims and their families.

"On behalf of the United States, I express my condolences to the victims and their families. The American people send their thoughts and prayers to the people of the United Kingdom. We condemn these horrific acts of violence, and whether they were carried out by troubled individuals or by terrorists, the victims know no difference," a statement from Tillerson's office said.

Earlier, U.S. President Donald Trump described the incident as "big news" after he was updated on the situation. He is also said to have called U.K. Prime Minister Theresa May following the attack.

Four people died, including a police officer, and at least 20 people were injured in a major terror attack outside the Houses of Parliament in London.

Mark Rowley, the head of counter-terrorism at the Met, said the police officer, who was stabbed by a lone attacker attempting to enter the House of Commons, had succumbed to his injury. The suspect was also shot and killed as reported by The Guardian.

Earlier, at least 20 people, including three officers, were hurt when an attacker drove a vehicle into pedestrians on Westminster Bridge, near the Parliament.

One woman is believed to have been thrown over the bridge into the river Thames - and later pulled alive from the water - while another fell on to a hard surface below the bridge.

Speaking to reporters outside the central London hospital, junior doctor Colleen Anderson from St Thomas' hospital said a female pedestrian had also died.

Here are the top developments so far:

. The flag above Scotland Yard was flown at half mast to honour the heroism of its fallen officer and other victims of today's attack

. King's College Hospital confirmed that the major trauma unit have treated eight victims, six males and two females.

. Steve White, chair of the Police Federation of England and Wales, which represents tens of thousands of rank-and-file officers, paid tribute to the officers involved in the incident

. Former prime minister David Cameron also tweeted to express shock over the incident

. London mayor Sadiq Khan issued a statement saying that an urgent investigation is underway and his thoughts are with those affected and their families. He also expressed his thanks to the police and emergency services for their rapid response

. Tourists riding the London Eye were stranded on the iconic attraction when the area was locked down after a terrorism incident near the Parliament

. Conservative MP Tobias Ellwood gave mouth-to-mouth resuscitation to the policeman who was stabbed

. The Met police are appealing for pictures or video footage of the incident

. Intelligence agencies have immediately put together teams to work on identifying who was involved in the attack and whether there was a link to a terrorist group

. A police officer was stabbed and his attacker shot after a major terrorist incident at the Houses of Parliament in which several people have been injured

. The attacker mowed down several pedestrians as he drove a grey Hyundai i40 across Westminster Bridge before crashing it into railings then running through the gates of the Palace of Westminster and stabbing the officer

. Witnesses said he was shot by police as he approached a second officer while clutching his knife

. The Port of London Authority confirmed that a seriously injured woman has been recovered from the Thames river, however, it is yet to be confirmed if she fell or jumped from the bridge

. The House of Commons has been put in lockdown, with many MPs confined to the Commons chamber after parliamentary business was suspended

. Plans for a London-wide emergency have been put into place as a precaution, but police are hopeful the incidents are over

. A Downing Street source confirmed to Guardian that Prime Minister Theresa May was "okay". May was seen being ushered into a silver Jaguar car as what sounded like gunfire rang out at parliament during the incident at around 2.45pm

. The police say no terrorists have got into the parliament building. They say two have been caught on Westminster Bridge, and one officer is down

. It has been confirmed that at least 10 patients have been treated for injuries on the Westminster Bridge

. The London Eye, opposite the House of Parliament on the other side of Westminster Bridge, is also in lockdown, with some being held inside the attraction's pods

More details to follow.