US president-elect Donald Trump has accused Barack Obama of creating "inflammatory" roadblocks during the transition of power in America.
Mr Trump also accused the outgoing administration of treating Israel with "total disdain", further straining the veneer of civility between the incoming and outgoing leaders.
Although Mr Trump did not detail his complaints in a series of broadsides on Twitter, he made it clear that Mr Obama's recent claim that he would have won the election had he been running did not sit well with the president-elect.
Mr Trump's largely respectful tone about the current president since the election evaporated in his latest tweets.
He tweeted: "Doing my best to disregard the many inflammatory President O statements and roadblocks.
"Thought it was going to be a smooth transition - NOT!"
Mr Trump also took direct issue with the Obama administration's decision to let a UN Security Council resolution critical of Israel pass.
"We cannot continue to let Israel be treated with such total disdain and disrespect," he said in a two-part tweet.
"They used to have a great friend in the U.S., but ... not anymore. The beginning of the end was the horrible Iran deal, and now this (U.N.)! Stay strong Israel, January 20th is fast approaching!"
Mr Trump and his team have until now been largely complimentary of the way Barack Obama and his team have handled the transition.
The US president-elect's complaints about the treatment of Israel came a few hours before John Kerry was due to make his final speech about peace in the Middle East as secretary of state - remarks which some Israeli officials panned in advance.
The administration's decision not to veto the UN resolution has aggravated an already strained US-Israel relationship.
A dispute erupted between Mr Obama and Mr Trump, spurred by Mr Obama's hypothetical musings that, had he run again, he would have been victorious.
Mr Obama suggested he still holds enough sway over the coalition of voters who elected him twice to get them to vote for him once again.
Mr Trump's response to that was: "NO WAY!"
The president-elect tweeted: "President Obama campaigned hard (and personally) in very important swing states, and lost. The voters wanted to MAKE AMERICA GREAT AGAIN!"
Mr Obama swept most key swing states in his two bids for the White House, but Hillary Clinton fell short in her battle with Mr Trump in the autumn.
Mr Trump also thanked himself for a surge in a key gauge of consumer confidence. He wrote on Twitter that the Conference Board had reported that its consumer confidence index had climbed to 113.7 in December.
Mr Trump noted that is the highest the index has climbed in more than 15 years, then added: "Thanks Donald!"