President Barack Obama said here on Monday that the US government has not yet got "all answers" about the explosions that rocked Boston, Massachusetts earlier in the day, but vowed to hold anyone behind them accountable.

In a live televised statement from the White House, Obama acknowledged that his government still did not know "who did this or why."

The president did not call the explosions a terror attack, and told the people not to "jump to conclusions."

But he stressed that those who were responsible for the incident "will feel the full weight of justice."

"We will find out who did this and we will hold them accountable," said Obama.

At least two people were killed and dozens of others injured in three explosions that took place during the Boston Marathon on Monday afternoon -- two near the finish line of the race and one at the Boston JFK Presidential Library.