"Here is what we know so far. Evidence indicates that the plane was shot down by a surface-to-air missile that was launched from an area that is controlled by Russia-backed separatists inside of Ukraine," he said.
"It's too early to guess what the intentions of those who launched these missiles. What we know right now, that a surface to air missile was fired. The shot was taken within the territory that is under the control of the separatists," Obama said, adding that the US is talking to the international community on this issue.
Obama, who spoke with his Russian counterpart Vladimir Putin, blamed Russia for the incident, saying that Russia provided sophisticated surface-to-air missiles to the Ukrainian separatist.
"He (Putin) has the most control over the situation. He has certainly not exercised (that)," Obama said.
"We also know that this is not the first time a plane has been shot down in eastern Ukraine. Over the last several weeks Russian-backed separatists have shot down a Ukrainian transport plane and a Ukrainian helicopter, and they claimed responsibility for shooting down a Ukrainian fighter jet.
Moreover, we know that these separatists have received a steady flow of support from Russia," Obama said.
Noting that this is a wakeup call for the international community, Obama warned that this tragic event would have consequences.
Describing the death of nearly 300 people on board the plane as "an outrage of unspeakable proportions", Obama said, "Our thoughts and prayers are with his family for this terrible loss," he said.
"This was a global tragedy.....So there has to be a credible international investigation into what happened. The UN Security Council has endorsed this investigation, and we will hold all its members, including Russia, to their word," he said.
He also called for an immediate ceasefire between separatist and the government in Ukraine.
"In order to facilitate that investigation, Russia, pro-Russian separatists and Ukraine must adhere to an immediate cease-fire. Evidence must not be tampered with.
Investigators need to access the crash site," Obama said.
The US he said stands ready to provide any assistance that is necessary.
"We've already offered the support of the FBI and the National Transportation Safety Board, which has experience in working with international partners on these types of investigations. They are on their way, personnel from the FBI and the National Transportation Safety Board," noted.
Obama said this outrageous event underscores that it is time for peace and security to be restored in Ukraine.
"For months we've supported a pathway to peace, and the Ukrainian government has reached out to all Ukrainians, put forward a peace plan and lived up to a cease-fire, despite repeated violations by the separatists, violations that took the lives of Ukrainian soldiers and personnel," he said.
Alleging that time and again, Russia has refused to take the concrete steps necessary to de-escalate the situation, Obama said he spoke to Putin on Thursday in the wake of additional sanctions that US has imposed.
"He said he wasn't happy with them, and I told him that we have been very clear from the outset that we want Russia to take the path that would result in peace in Ukraine, but so far, at least, Russia has failed to take that path.
"Instead, it has continued to violate Ukrainian sovereignty and to support violent separatists. It has also failed to use its influence to press the separatists to abide by a cease-fire. That's why, together with our allies, we've imposed growing costs on Russia," he said.
Obama said violence and conflict inevitably lead to unforeseen consequences.
"Russia, these separatists, and Ukraine all have the capacity to put an end to the fighting. Meanwhile, the United States is going to continue to lead efforts within the world community to de-escalate the situation, to stand up for the sovereignty and territorial integrity of Ukraine and to support the people of Ukraine as they courageously work to strengthen their democracy and make their own decisions about how they should move forward," he said.