After facing criticism in the U.S. about President Barack Obama's absence from the massive unity rally in Paris, the White House admitted Monday that it should have sent a high-profile representative to the event on Sunday.

More than 40 world leaders attended the demonstration of solidarity, called the biggest public gathering in France's history, and American reporters, pundits and some on Capitol Hill have been wondering why Obama was not among them.

"I think it’s fair to say we should have sent someone with a higher profile to be there," White House press secretary Josh Earnest said at the daily briefing Monday afternoon. "That said, there is no doubt that the American people and this administration stand foursquare behind our allies in France as they face down this threat."

French President François Hollande walked arm-in-arm with German Chancellor Angela Merkel and Mali's President Ibrahim Boubacar Keita during the rally. Israeli Prime Minister Benjamin Netanyahu and Palestinian leader Mahmoud Abbas, in a powerful act of unity, were also links in the chain of high-profile figures as they led the sombre procession.

Public Safety Minister Stephen Blaney represented Canada in the march, his office confirmed.

Why didn't Obama go? It's a question, and a headache, the White House started dealing with Sunday in the aftermath of what turned out to be a stunning display by millions of people in Paris and across the country who wanted to honour the 17 victims of three days of bloodshed in France.

If Obama couldn't go, why didn't the White House make sure the U.S. was represented by Vice-President Joe Biden, or Secretary of State John Kerry, or Attorney General Eric Holder who was actually in Paris for meetings?

Earnest said he wasn't in a position to explain the logistics of how decisions are made at the White House, but he did say it was the White House's responsibility to ensure proper U.S. representation at world events.

Obama would have liked to attend

In terms of the president going, he noted the extraordinary security requirements that must be met whenever Obama attends public events. His appearance can impact the public severely and Earnest suggested that in this case, while the Secret Service could have met the security challenges, Obama's attendance may have changed the nature of the event.

Planning for the event also only began on Friday, he noted. "Had the circumstances been a little different, I think the president himself would have liked the opportunity to be there," he said.

Obama spent the weekend in Washington, but Earnest said he did not have details about how the president spent his time. Biden also did not have any public commitments.

"The White House's explanation is pathetic," CNN host Fareed Zakaria said earlier in the day. "It's possible that you couldn't send Obama there — I thought this is why God invented vice-presidents."

He said the White House made a mistake when it judged that U.S. ambassador to France Jane Hartley's presence would be enough. She was one of the highest-level officials to attend, along with the assistant secretary of state for European affairs Victoria Nuland.

Republican Senator Ted Cruz wrote an op-ed for Time magazine's website saying Obama, or someone important from the White House, "should have been there."

"The absence is symbolic of the lack of American leadership on the world stage, and it is dangerous," the Texas senator wrote.

Before admitting it should have done things differently, the White House had said the U.S. was represented by Hartley and by Holder, who was in meetings, not at the march.

Kerry will visit Paris this week

Administration officials are also pointing to what Obama has done to show solidarity with France since the deadly attacks in Paris, including his visit to the French Embassy in Washington where he signed a book of condolences, his personal phone call to Hollande, his written statement and public comments on two separate days last week.

U.S. Secretary of State John Kerry gives the traditional Indian greeting before departing Ahmedabad, India, on Monday. Kerry told reporters he wanted to attend Sunday's rally in Paris but couldn't and instead will travel there later this week. (Rick Wilking/Associated Press) U.S. security, intelligence and terrorism officials have been working with their French counterparts and the administration is extremely engaged in the developments out of France, White House officials say.

Kerry didn't go to Paris on Sunday because of a pre-planned trip to India which is where he is spending most of Monday. He will go to the French capital later in the week.

He told reporters in India that he very much wanted to be in Paris on Sunday and he tried to downplay any controversy that Obama's or his absence is generating.

"This is sort of quibbling a little bit in the sense that our assistant Secretary of State Victoria Nuland was there and marched, our ambassador was there and marched, many people from the embassy were there and marched."

The White House's defence of how it is handling the Paris attacks and its judgment call on who would attend the unity march won't stop the questions from being raised, however, or the criticism, which is mostly coming from home, not from France.

The U.S. ambassador to France told CNN on Monday morning that Hollande personally thanked her on Sunday when she saw him, for the U.S.'s support and co-operation, and that all the officials she has been in touch with have expressed nothing but gratitude.

"If you talk to the French, they think we have been unbelievably supportive," she said.