Donald Trump and Vladimir Putin arrive for a meeting in Helsinki in July 2018

Donald Trump has called off expected bilateral talks with Vladimir Putin at the G20 summit in Buenos Aires amid increasing tensions surrounding the Russia-Ukraine crisis and explosive reports the president's former lawyer lied about a Trump Tower project in Moscow.

As world leaders began to arrive in Argentina ahead of the start of the summit on Friday, tensions surround Russia's current stand-off with Ukraine over the Kerch Strait in the Sea of Azov, where the Russian navy captured three of its neighbours vessels over a territorial dispute on Sunday. Mr Trump tweeted while on his way to the annual summit that he was cancelling his meeting with Russian President Vladimir Putin, writing, "Based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting in Argentina with President Vladimir Putin."

German chancellor Angela Merkel is expected to address the situation, which has seen Ukraine implement martial law in 10 regions, before Mr Trump and Mr Putin sit down on Saturday, as well as other worlds leaders, who plan to discuss the conflict along with a multitude of other high-profile global concerns. But, in a quirk that shows that international travel is never easy, Ms Merkel's plane was forced to make an unexpected landing in Germany — and she will not be able to attend the opening of the G20 summit.

Beyond the situation in Ukraine, the stakes are high for those attending, and that is especially true for Mr Trump, who is hoping to finish signing a reworked trade deal with Canada and Mexico — and find common ground with China to try to divert a potential escalation in trade relations that has already led to tariffs on hundreds of billions of dollars in imports for both countries. Days before the G20, Mr Trump suggested that failure to negotiate adequately during a dinner with Chinese President Xi Jinping could lead to even further tariffs.

Meanwhile, the meeting is the first high profile meeting of world leaders since the killing of journalist Jamal Khashoggi by Saudi officials in Turkey, and world leaders are taking varied approaches in how they deal with Saudi Crown Prince Mohammed bin Salman, who has been accused of overseeing the murder of the journalist. Mr Trump is not expected to meet with the crown prince, while French President Emmanuel Macron is going ahead with a meeting. Canadian Prime Minister Justin Trudeau has said that he would not schedule a meeting with the Saudi leader.

In Buenos Aires, security has ben ramped up as officials prepare for the high profile summit, and residents of the city have been advised to take a long weekend away if possible. Meanwhile, thousands of anti-capitalist protesters are expected in the city.