Washington (CNN) President-elect Donald Trump isn't waiting until Inauguration Day to assert his posture on foreign policy, even in areas plainly at odds with the sitting commander-in-chief.

On sensitive issues of diplomacy and national security, Trump has displayed a continued willingness to pressure and contradict President Barack Obama, eschewing a "one president at a time" policy that Obama insists must govern the peaceful transition of power.

The most forceful example came Thursday, as diplomats at the United Nations were preparing for a vote in the Security Council on a resolution rebuking Israel for its settlement activity in the West Bank and East Jerusalem. In a morning statement, Trump urged Obama to reject the measure, arguing it "puts Israel in a very poor negotiating position and is extremely unfair to all Israelis."

The vote was postponed. But at the time Trump's statement emerged, the Obama administration was still debating whether to abstain and let the measure pass, a gesture that would have been in line with the White House's vocal objections to settlement activity on lands claimed by the Palestinians.

Trump's team informed Obama administration officials ahead of time they were planning to release the statement, according to Jason Miller, a transition spokesman. A national security spokesman for the White House declined to characterize how the message was received.

But administration officials privately say the move, paired with a string of public splits between Trump and Obama, runs afoul of a longstanding custom observed by past incoming presidents to withhold statements or remarks that might be seen as contradictory to the sitting administration and perplex global allies as they await a new commander-in-chief.

"The President-elect clearly is determined to show through any number of moves during the transition that, in effect, there's going to be a sharp break with the policy toward Israel of his predecessor," said Aaron David Miller, a vice president at the Woodrow Wilson Center and a CNN global affairs analyst.

"I think this is unprecedented for a President-elect during a transition to openly oppose an act of diplomacy at the UN in real-time in an administration," Miller said. "It's remarkable."

Trump's team respects the one president at a time concept, but that doesn't mean he will sit back until January 20, his incoming White House press secretary Sean Spicer said on CNN's "New Day" Friday morning.

"President Obama and his team have been unbelievably gracious to the President-elect and his team, but at the end of the day, he's not someone that's going to sit back and wait," Spicer said.

"(Trump's) point was Israel is our closest ally in the Middle East," Spicer said. "It is something that we should protect and he wanted to make it very clear that anything that undermined Israel, which is a great friend of the united states, he was going to make sure his voice was heard. and it worked. But look, what is the hit, that he's been unbelievably successful so far as a President-elect?"

Obama held back from meetings in 2008

During Obama's own transition to power in 2008, he withheld extensive public comment about flashes of violence in the Middle East and terror attacks in India that occurred as President George W. Bush was concluding his term.

Bush's aides even invited Obama to participate in a Group of 20 meeting held in Washington shortly after he was elected President. Obama's team -- which at the time was developing an economic recovery plan that differed from Bush's proposals -- concluded his presence at the summit could send contradictory signals to global allies.

Trump, meanwhile, has shown little signs of concern about sending mixed signals about US policy to overseas allies. He's offered foreign policy prescriptions on Twitter and in public remarks that differ from Obama's approach. And he's claimed to be openly negotiating government contracts before he takes office.

This week alone has seen Trump meet with top members of the US military at his Florida estate, followed by a session with the chief executives of Boeing and Lockheed Martin. Trump had lambasted the cost of projects those firms are completing for the US government, later claiming credit during a rally for negotiating down the costs of a new presidential aircraft.

On Thursday he tweeted the US "must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes," a break from Obama's own policy of reducing nuclear weapon stockpiles. Later, a spokesman clarified Trump was referencing "the threat of nuclear proliferation and the critical need to prevent it."

Russia and China

The most glaring divide between the incoming and outgoing administrations: Trump's stance on Russia, who the US accuses of meddling in the presidential election. Trump has questioned the intelligence that led to that assessment, leading to a combative public spat between his transition team and the White House.

Disputes over how to handle China have also emerged. When China seized a US underwater drone in international waters this week, the President-elect responded forcefully on Twitter, including making suggestions to the current administration on how to proceed.

"We should tell China that we don't want the drone they stole back.- let them keep it!" Trump wrote. The drone was returned earlier this week.

The messages came after another diplomatic scuffle prompted by Trump's phone conversation with the leader of Taiwan, a move that broke decades of US diplomatic precedent and sparked bombast in Beijing.

Obama himself brushed off the incident in a press conference last week, indicting that Trump's move in itself wasn't necessarily harmful.

But he advised his successor to carefully weigh the consequences of his actions, and insisted that US foreign policy was still under his control for another month.

"What I've advised the President-elect is that across the board on foreign policy, you want to make sure that you're doing it in a systematic, deliberate, intentional way," Obama said. "And since there's only one President at a time, my advice to him has been that before he starts having a lot of interactions with foreign governments other than the usual courtesy calls, that he should want to have his full team in place, that he should want his team to be fully briefed."