President Obama on Tuesday mourned the lives lost in the Boston Marathon bombing a year ago and praised the “compassion, kindness and strength” of those who rushed to help the wounded.

“A year ago, tragedy struck at the 117th Boston Marathon. Four innocent people were killed that week, and hundreds more were wounded,” said Obama in a statement, marking the one-year anniversary of the deadly attack. “Today, we remember Krystle Campbell, Lingzi Lu, Martin Richard, and Sean Collier. And we send our thoughts and prayers to those still struggling to recover."

The president also paid tribute to those who came to the aid of those hurt.

“We also know that the most vivid Images from that day were not of smoke and chaos, but of compassion, kindness and strength: A man in a cowboy hat helping a wounded stranger out of harm’s way; runners embracing loved ones, and each other; an EMT carrying a spectator to safety,” said Obama.

“Today, we recognize the incredible courage and leadership of so many Bostonians in the wake of unspeakable tragedy. And we offer our deepest gratitude to the courageous firefighters, police officers, medical professionals, runners and spectators who, in an instant, displayed the spirit Boston was built on — perseverance, freedom and love,” he added.

“One year later, we also stand in awe of the men and women who continue to inspire us — learning to stand, walk, dance and run again. With each new step our country is moved by the resilience of a community and a city,” Obama continued. “And when the sun rises over Boylston Street next Monday — Patriot’s Day — hundreds of thousands will come together to show the world the meaning of Boston Strong as a city chooses to run again.”

The president will also observe the anniversary of the Boston attack with a moment of silence in the Oval Office with his aides, according to the White House. The moment is planned for 2:49 p.m., exactly a year after two pressure cookers packed with shrapnel exploded near the finish line of the Marathon, killing 3 runners and spectators.

The suspects in the attack, Dzhokhar and Tamerlan Tsarnaev, are also suspected in the murder of MIT police officer Sean Collier as they avoided law enforcement during a massive manhunt. Tamerlan was killed in a shoot-out with police, while his brother is in prison awaiting trial for the bombing.

Vice President Joe Biden and his wife, Dr. Jill Biden, will attend a memorial service in Boston on Tuesday.