Prime Minister Liz Truss will vow to match UK spending on military support to Ukraine next year, as she restarts her government's agenda following the Queen's funeral.
Ms Truss will pledge military aid worth billions during a trip to meet world leaders in New York this week.
She will use a speech to the UN General Assembly to rally support for Ukraine.
The trip comes at a time of global economic turmoil driven by soaring energy prices and the Ukraine war.
The UK has been one of the leading donors of military aid to Ukraine, committing £2.3bn since Russian President Vladimir Putin's forces invaded the country in February.
A hectic week of diplomacy and policy announcements lies ahead for Ms Truss and her government after a period of national mourning for the late Queen ended.
Political activity and government business were paused until after the Queen's funeral, which was attended by Ms Truss, alongside other politicians, foreign dignitaries and members of the Royal Family.
As politics resumes in the UK, Ms Truss has travelled to the United States for her first foreign trip as prime minister.
Speaking to reporters during the flight to New York, Ms Truss said she was "hugely honoured" one of the Queen's final acts as monarch had been to invite her to form a government.
Ms Truss's agenda will include a series of meetings with world leaders, including US President Joe Biden and French President Emmanuel Macron, and her first big speech as prime minister on the international stage.
She is expected to meet Mr Biden on Wednesday at the assembly after a planned meeting with him before the Queen's funeral was postponed.
Asked about the prospect of a future trade deal with the US, Ms Truss said negotiations were not taking place currently and she did not expect any "in the short to medium term".
Ahead of her meeting with Mr Macron, Ms Truss said she wanted to have a constructive relationship with France and there were a number of issues they need to work together on.
Prepare for the roaring return of politics.
Families, businesses, the country face grave threats: soaring prices, crippling fuel costs, the prospect of recession.
But, with the funeral now over, the arguments resume - and the demands for action will be loud.
The prime minister is already on her first foreign trip in the job.
It will mean the returning political conversation will have a diplomatic air - in its opening few hours at least - rather than an immediately intense domestic scrappiness.
But that will be back before you know it.
Ms Truss's speech to the assembly will focus on renewing the UK's long-term commitment to Ukraine and ending international energy dependence on Russia.
In her speech, Ms Truss will point to the recent success of Ukraine's counter-offensives as examples of what the country can achieve with Western backing.
"Ukraine's victories in recent weeks have been inspirational," Ms Truss said. "Time and time again these brave people have defied the doubters and showed what they can do when given the military, economic and political support they need."
Supporting Ukraine was a key policy plank of the previous UK government led by Ms Truss's predecessor, Boris Johnson.
On a visit to Ukraine last month, Mr Johnson said the West must endure rising energy bills to help the country drive out Russia.
But Labour urged Ms Truss to use the trip to the UN to start "rebuilding our country's diplomatic influence".
Shadow foreign secretary David Lammy, also attending the assembly, said: "Twelve years of Conservative governments making diplomatic gaffes, announcing plans to break international law, failing to live up to promises on climate action and cutting international aid have damaged relations with the US and left Britain isolated on the global stage.
"After being snubbed by the Biden administration within her first weeks in office, Liz Truss urgently needs to wake up to the damage her reckless approach to foreign policy is doing to the UK's national interest."
A busy schedule
Domestic politics in the UK has been on hold, while the country mourned the loss of the late Queen.
Her death occurred during Ms Truss's first few days as prime minister, and halted the usual business of government, including a ministerial reshuffle.
MPs will return to Parliament on Wednesday, when they can swear a new oath of alliance to King Charles III, if they wish.
Business Secretary Jacob Rees-Mogg is expected to set out government's energy support package for businesses, but this is yet to be confirmed.
The package was part of a plan to limit energy bill rises for businesses and all households for two years, unveiled hours before the Queen's death was announced.
On Thursday, Heath Secretary and Deputy Prime Minister Thérèse Coffey is due to make an announcement about her plan for the NHS this winter.
A mini-budget, described as a "fiscal event" to outline the government's economic plans, will then take place on Friday.
In it, Chancellor Kwasi Kwarteng is expected to deliver tax cuts promised by Ms Truss during her campaign to be Conservative Party leader.
Ms Truss has promised to use the mini Budget to undo a rise in National Insurance and cancel a planned hike in corporation tax.
She has also said she would temporarily scrap green levies on energy bills to bring down prices for consumers.
Source: BBC
BDST: 1147 HRS, SEP 20, 2022
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