Melania Trump has said her husband 'is doing the best that he can' in a second term besieged by wars in Iran and Ukraine.

The First Lady gave the guarded verdict on Fox News Wednesday, the morning after Trump's speech to the United Nations General Assembly in New York.

'He's very focused. He has a lot on his plate. It's very different, what's going on around the world now. But I think he's doing the best that he can,' Melania said of his second administration. 

'He works nonstop. He has the most energy than anybody. He's from morning until evening nonstop working,' she added.

Host Brian Kilmeade noted that Trump often solicits her opinion after his speeches and interviews, and asked for her appraisal of the president's UN performance.

'I told him he had great delivery, he did very well. And a great speech,' she said. 

'I tell him the truth. Sometimes he doesn't want to hear it, what I tell him, but that's okay. I always say the truth,' she added. 

Melania was in the hall at UN headquarters on Tuesday as her 80-year-old husband threatened to 'annihilate the Islamic Republic' of Iran and urged world leaders to join him in enforcing its 'complete economic isolation.'

Trump also broke off mid-speech to hunt for his wife in the chamber after crediting her with securing the return of 'many displaced Ukrainian and Russian children'. 

'Where is our First Lady? Where is she? She's around here someplace. Can you imagine? I can't see the First Lady,' he said. 

Melania was on Fox to launch Imperia, a women's leadership summit the hosts billed as a 'Davos for executive women', before ringing the opening bell at the New York Stock Exchange at 9.30am. Fox News Media is a partner on the event. 

She told the hosts she has 'a direct channel with Russia, and with Ukraine' and that her representative is working on reuniting more children displaced by the war with their families. 

Trump told the UN he was 'working very closely with the leaders of Russia and Ukraine, and we will get that one done.'

He met Volodymyr Zelensky on the sidelines on Tuesday, when the Ukrainian president asked for a 'winter package' of new weapons including Patriot missile defense systems, according to the Wall Street Journal. 

Trump has been pleading with Zelensky to end strikes on Russian oil refineries after US diesel prices hit record highs. Russia supplies around 10 percent of global seaborne-traded diesel.

The deepening crisis is adding pressure to global energy markets already strained by the war in Iran, with Tehran-backed Houthi militants tightening their grip on the Bab el-Mandeb Strait - the strategic waterway between Yemen and the Horn of Africa.

Trump said his envoys envoys Jared Kushner and Steve Witkoff held 'very productive' talks with the Iranian UN delegation aimed at ending the war. 

Melania also used her Fox interview to trail a new two-part docuseries, which she said would include 'some private questions that I will answer that people never heard before.' 

'It's more conversation one on one with me,' she said, adding that the series could land in November but no date had been set. 

It follows her documentary Melania, directed by Brett Ratner and distributed by Amazon Prime Video. 

Trump is due to greet Chinese President Xi Jinping on the tarmac at Joint Base Andrews on Wednesday, his first state visit to Washington in 11 years. 

'He decided to because they have a great relationship and he's coming on our soil and we need to welcome them with the most respect,' Melania said. 

She said she will take Xi's wife Peng Liyuan to the Smithsonian on Thursday, ahead of the state dinner that night. The couples are then due to take tea at the White House on Friday before touring the National Archives together.