This is a transcript of today's press conference with Sir Ian Blair and Andy Hayman.
As you are aware there is a lot of police activity going on today in relation to the underground and bus incidents of yesterday. This is a very, very fast moving investigation.
Andy Hayman is going to make an appeal for new information. I have a few points that I would like to make to begin with. As I've said before, this is the greatest operational challenge ever faced by the Metropolitan Police Service. The MPS and its sister services are doing a magnificent job, but officers are facing previously unknown threats and great danger.
We need the understanding of all communities, and the co-operation of all communities, and we need calm. We know that there are rumours sweeping London, and I really do appeal for people to listen to the facts as they emerge. We remain resolute, and will work tirelessly, and imaginatively with every community in London to solve this crime. The most important message we have other than this appeal is that this operation is targeted against criminals. It is not targeted against any community, or any section of the community. There are hundreds of police officers working across London on these inquiries and the anti-terrorist teams are working literally around the clock and there probably won't be a let-up in that for some considerable time.
I can say as part of operations linked to yesterday's incidents, Met police officers have shot a man inside Stockwell Underground Station at approximately 10am this morning. London Ambulance Service and the air ambulance both attended and the man was pronounced dead at the scene. I understand Stockwell tube station remains closed.
The information I have available if that this shooting is directly linked to the ongoing and expanding anti-terrorist operation. Any death is deeply regrettable. I understand the man was challenged and refused to obey. I can't go any further than that at this stage, and I am now going to hand over to Assistant Commissioner Andy Hayman.
AC Andy Hayman; I would like top start of by reminding everyone, that about two weeks ago we stated our objectives for this investigation. The object is to identify and successfully prosecute the people responsible for these events. The resolve to achieve that objective has never been stronger. The energy and enthusiasm of both the community and our officers is at its height.
The purpose of today is to set out what we have done since yesterday's events, which has then led us to asking the community for their help. It was said yesterday by colleagues that following such an event as yesterday evidence opportunities and intelligence opportunities increase. That is the case.
Since yesterday we have been very busy - analyzing CCTV tapes, taking numerous statements and conducting house to house enquiries. This has been fruitful, because this afternoon we are going to be issuing CCTV images of four men we urgently want to trace in connection with attempts to detonate four explosive devices on the transport system in central London yesterday.
It is crucial that detectives are able to question them about yesterday's events at the Oval, Shepherds Bush, Warren St underground station and on a Route 26 bus in Hackney Road at the junction with Colombia Road, E2.
I want to be very clear now about what I want the public to do. There are two requests here.
Firstly anyone who has information about where these men currently are - you should immediately call 999 and ask for urgent police response. The public are asked not to approach them.
If anyone knows they believe the identities of these men, or has other information about them or their movements, they should contact the confidential Anti-Terrorist Hotline on 0800 789 321.
What I would like to do now is deal with all scenes individually and describe to you about the events that occurred there and also show you the images that a relevant to those scenes.
At the Oval underground station a device was left in a carriage on a Northern line train traveling northbound. The image we are now showing shows a man running away from the northern line at the Oval underground station at approx 12:34hrs yesterday.
We believe this man had traveled northbound on the northern line from Stockwell underground station to the Oval. He was wearing a dark top with the words 'New York' written in white across the front. This top was later found in Cowley Road, Brixton.
A device was left at the rear of the top deck of the Route 26 bus travelling from Waterloo to Hackney Wick. The image that is now showing is of a man at the rear of the top deck on that bus at about 12:53.
He got off the bus at Hackney Road at approximately 1306hrs. He was wearing a grey t-shirt with what appears to have a palm-tree design on the front and a dark jacket with, and a white baseball cap.
At Warren Street a device was left in a carriage on the northbound Victoria line. The image that is now showing of the third person we want to identify shows a man leaving Warren Street underground station at approximately 12:39. He was wearing dark clothing.
Finally, at Shepherd's Bush a device was left on a Hammersmith & City line train travelling westbound. This final image that is showing is of a man at Westbourne Park underground station at approximately 12:21. We believe he then travelled westbound on the Hammersmith & City line to Shepherd's Bush underground station where he ran from the station. He was wearing a dark shirt and trousers and was later reported to be wearing a white vest.
Yesterday's incidents do bear similarities to the bomb attacks in London on July 7th in as much as there were three underground trains and a bus that were targeted. There are other features that are emerging which are also of interest to detectives.
We are actively pursuing lines of enquiry you are aware that earlier today, this afternoon, we were entering a house in central London.
What this demonstrates is how fast moving this investigation is and how hopefully productive the lines of enquiry are.
Initial forensic examination indicates that a bomb partially detonated at each of the four sites. At this stage it is believed that the devices consisted of home-made explosives and were contained in dark coloured bags or rucksacks.
At this stage it is too early to tell how these were detonated.
I am urgently seeking the public's assistance. It is time to do what the public are very good at - which is support investigations.
It is for us to decide whether any info that is given is of relevance. So if someone thinks it may be relevant - we would ask them to contact us as we have guided.
I would just like to pose a couple of questions which might help people think through this request:
Do you recognise any of these men?
Did you see them at the three underground stations or on the bus?
Did you see them at a different location?
Did you see these men together before or after the incidents?
Did you see them with anyone else?
If I can remind you - if you see these men, the public response should be to ring 999 and not approach them yourselves.
If you believe you know the identity of these men or have information relevant to those questions a different response is required - that is to ring the Anti-Terrorist Hotline on 0800 789 321.
I would like to place on record my congratulations to Andy and his team - for the speed at which they have reached this stage of the investigation.
Just two final messages from me.
The first one is this reiteration of the need for calm and the need to understand that rumours will sweep around about what is happening. At the moment the situation is under control and the investigation is proceeding. The scenes are under control and the house being searched is under control and the second crucial message is that we can only defeat this form of terror is by working with communities, by getting the communities support in to everything that we are doing. We will try and explain everything that we possibly can - but it is a very very fast moving scenario and we can only do that from time to time.
I am very grateful to people of London for the way in which they have reacted so far. I hope very much we will be able to bring this to as swift a conclusion as possible.