Around 800,000 American civil servants aren’t being paid and museum’s, national parks and other services provided by the US federal government remain closed.
President Trump sent a letter to Ms Pelosi on Thursday, just before she and other politicians were set to depart on the previously undisclosed trip. In the letter President Trump belittled the trip as a "public relations event" and said it would be best if Pelosi remained in Washington to negotiate to reopen the government.
"Obviously, if you would like to make your journey by flying commercial, that would certainly be your prerogative," Donald Trump wrote.
The political tit-for-tat between President Trump and Ms Pelosi laid bare how the US government-wide crisis has devolved into an intensely pointed clash between two leaders determined to prevail.
Ms Pelosi’s spokesman Drew Hammill told journalists that she planned to travel to Afghanistan and Brussels to thank service members and obtain briefings on national security and intelligence "from those on the front lines."
Mr Hammill also noted that President Trump had traveled to Iraq during the shutdown, which began Dec. 22.