Rishi Sunak spoke to German Chancellor Olaf Scholz on Friday evening, said a No10 spokesperson, when both leaders "agreed on the importance of allies continuing to support Ukraine’s defence".
The conversation came a week after Mr Sunak signed a deal pledging the UK would provide £2.5 billion in military aid to Ukraine over the next year, to help in its war against Russia.
“Prime Minister Rishi Sunak spoke to the German Chancellor Olaf Scholz this evening," said a No10 spokesperson on Friday.
“The Prime Minister updated on his recent visit to Kyiv, including the signing of the UK-Ukraine Agreement on Security Cooperation and the UK’s announcement of £2.5 billion in further military aid for Ukraine.
“They agreed on the importance of allies continuing to support Ukraine’s defence, which is vital for European and global security, and providing the Ukrainian armed forces with the weapons they need to defeat Russia’s invasion.
"The leaders also discussed wider cooperation on defence and security, including on supporting regional stability in the Middle East.
“Both leaders discussed the shared European challenge of illegal migration, noting the importance of strong joint action across the continent to deal with criminal people smuggling gangs.
"They agreed to continue working closely together on this issue, including through Italy’s presidency of the G7.”
Last week, Mr Sunak and Ukrainian president Volodymyr Zelensky signed a security deal between the UK and Ukraine, as the British Prime Minister made a surprise visit to Kyiv.
Mr Sunak pledged the UK “will not falter” in its commitment to Ukraine, as he said the Government would provide £2.5 billion in military aid for the country's fight against Russia over the coming year.
It will fund long-range missiles, air defence, artillery ammunition and maritime security.
About £200 million will be spent on a push to procure and produce thousands of military drones, many made in the UK. It is expected to be the largest delivery of drones to Ukraine from any nation.
Mr Zelensky described it as an “unprecedented security agreement” and thanked Mr Sunak for his "personal leadership" after the pair signed the accord.The PM was awarded with the Ukrainian order of freedom honour recognising his "outstanding personal contribution into strengthening Ukrainian-British interstate co-operation, supporting state sovereignty and territorial integrity of Ukraine".
Mr Zelensky has been pressing allies in the West to provide more support to fight back against Russian aggression, amid fears that interest in the war is flagging as attention turns to the situation in the Middle East.
The crisis in Gaza as Israel continues to bombard the Palestinian territory has also turned global attention away from the battle against Putin.