President Volodymyr Zelensky has invited Chinese President Xi Jinping to visit Ukraine.
The prime minister embraced Mr Zelensky as he arrived at Stansted Airport on just his second overseas visit since the war broke out.
Mr Zelensky stressed that a meeting with Mr Putin made no sense.
Mr Niinisto arrived in Ukraine on Tuesday for his first visit since the beginning of the Russia-Ukraine conflict.
“We are determined to make sure that Ukraine has what it needs to succeed on the battlefield.”
NATO promised more arms and equipment for Ukraine to help restore power supplies cut by Russian strikes.
The journalists were banned by the Ukrainian military not to report from the recently recaptured Kherson region.
The Ukrainian government plans to scale down the number of ministries from 20 to 14 and reduce the number of civil servants.
UN secretary-general António Guterres wants to save an agreement on grain exports from Ukraine via the Black Sea, which Moscow suspended following drone attacks on its fleet.
Mr Reinsalu also asked the UK not to cut troop numbers in Estonia, saying, “we love UK soldiers” and “we want more.”