US President Joe Biden apologised after some members of the National Guard stationed at the Capitol were pictured sleeping in a car park.
More than 25,000 troops were deployed to Washington DC for his inauguration after violence earlier this month.
Images spread on Thursday showed them forced to rest in a nearby parking garage after lawmakers returned.
The conditions sparked anger among politicians, and some state governors recalled troops over the controversy.
Mr Biden called the chief of the National Guard Bureau on Friday to apologise and ask what could be done, according to US media reports.
First Lady Jill Biden also visited some of the troops to thank them personally, bringing biscuits from the White House as a gift.
“I just wanted to come today to say thank you to all of you for keeping me and my family safe,” she said.
Our troops deserve the utmost honor & respect for securing the Capitol & defending democracy this week.
This is unconscionable & unsafe. Whoever’s decision this was to house our National Guardsmen & women in underground parking lots must be held accountable. pic.twitter.com/mBwpoog6YC
— Tim Scott (@SenatorTimScott) January 22, 2021
Many voiced concerns about the conditions, with guardsmen exposed to car fumes and without proper access to facilities like toilets after having been on alert for days.
Images of the cramped conditions also sparked fears about the spread of coronavirus.
A Reuters report on Friday said between 100 and 200 of those deployed had tested positive for Covid-19.
A joint statement from the US National Guard and US Capitol Police on Friday said they had worked together to make sure those in the Capitol Complex had “appropriate spaces” to take on-duty breaks.
They also said off-duty troops were being housed in hotel rooms or other accommodation and thanked members of Congress for their concern.
Some 19,000 guardsmen will return to their home states in the coming days with about 7,000 expected to stay on in Washington, according to the New York Times.