"I have been engaged with our national security team and on the phone with president Poroshenko of Ukraine and in dealing with a very tragic circumstance, which you have probably already heard about.

"A Malaysian aircraft, heading from western Europe to Kuala Lumpur, as it crossed the border of Ukraine and Russia, apparently, and I say apparently because we don't have all the details, and I want to be sure of what I'm saying, apparently had been shot down. Shot down, not an accident. Blown out of the sky.

"We see reports that their may have been American citizens on board and obviously that's our first concern. And we are now working every minute to confirm those reports as I speak.

"This is truly a grave situation. Nearly 300 souls have been lost. The families have our consolation and our prayers. There are many of them who need answers, and we will get those answers and we will take the next steps accordingly. We are in touch with the Ukrainian government, I was on the phone as I said for the better part of half an hour with President Poroshenko, I'm in contact with our president, as well as our national security team.

"I offered president Poroshenko the help of our expertise our National Transportation Safety Board and other experts in the community. He accepted that help and they will be on their way rapidly to see if we can get to the bottom of this.

"I know you join me in prayers for the families of all the passengers, wherever they call home. It's important to get to the bottom of this sooner rather than later, because of the possible repercussions that could flow from this beyond the tragic loss of life. So that's why I was late and I apologise for it. But my heart goes out to those families."