The National Security and Defence Council announced the restrictions after Kyrylo Budanov, head of Ukraine's GUR military intelligence agency, presented the Council with evidence of Russian special services' ability to snoop on the platform, it said in a statement.
But Andriy Kovalenko, head of the security council's centre on countering disinformation, posted on Telegram that the restrictions apply only to official devices and not personal phones.
Telegram is heavily used in both Ukraine and Russia and has become a critical source of information since the Russian invasion of Ukraine in February 2022.
But Ukrainian security officials had repeatedly voiced concerns about its use during the war.
European Commission president Ursula von der Leyen is visiting Ukraine. (AP PHOTO)
Based in Dubai, Telegram was founded by Russian-born Pavel Durov, who left Russia in 2014 after refusing to comply with demands to shut down opposition communities on his social media platform VKontakte, which he has sold.
Durov was arrested upon landing in France in August as part of an investigation into crimes related to child pornography, drug trafficking and fraudulent transactions on Telegram.
The Security Council statement said Budanov had provided evidence that Russian special services could access Telegram messages, including deleted ones, as well as users' personal data.
"I have always supported and continue to support freedom of speech but the issue of Telegram is not a matter of freedom of speech, it is a matter of national security," Budanov said in his own statement.
According to the Telemetrio database, about 33,000 Telegram channels are active in Ukraine.
Ukrainian President Volodymyr Zelenskiy, who sits on the security council, as well as military commanders and regional and city officials all regularly publish updates on the war and report important decisions on their Telegram channels.
Ukrainian media have estimated that 75 per cent of Ukrainians use the app for communication and surveys suggest 72 per cent view it as a key source of information as of the end of last year.
Zelenskiy said on Friday during a visit by European Commission President Ursula von der Leyen that Ukraine's "victory plan" in the war depends on quick decisions being taken by allies this year.
He told a joint press conference with von der Leyen that Ukraine planned to use a proposed multi-billion dollar European Union loan for air defence, energy and domestic weapons purchases.
Zelenskiy singled out the importance of US President Joe Biden to the victory plan, which he said the two leaders will discuss when they meet.
The Ukrainian leader is travelling to the United States next week.
"Most of the decisions from the plan depend specifically on him (Biden). On other allies too but there are certain points which depend on the goodwill and support of the United States," Zelenskiy said.
Zelenskiy has provided regular updates on the plan's preparation but has given few clues to the contents, indicating only that it aims to create terms acceptable to Ukraine after more than two and a half years of war following Russia's full-scale invasion.
"The entire plan is predicated upon quick decisions from our partners. The plan is predicated upon decisions which should take place from October to December, and not delaying these processes," he told the press conference alongside von der Leyen.
Zelenskiy said in his nightly video address that he was counting on Biden's support for the plan, intended not only to bring peace but also strengthen his country.
"Ukraine is counting very much on this support," he said.
"And this is fair. Because when one nation wins the battle for its independence and adherence to international law, the whole world wins."
