The United States and Britain have not authorised Ukraine to use long-range missiles on targets inside Russia possibly fearing an "escalation", President Volodymyr Zelensky said.
Russian President Vladimir Putin has warned that firing long-range weapons into Russia would signify that NATO countries were at war with Moscow.
"Neither America nor the United Kingdom gave us permission to use these weapons on the territory of Russia, on any targets, at any distance," Zelensky told reporters late on Friday.
"I think they are worried about an escalation (of hostilities)," he said.
The weapons are supplied by Ukraine's Western allies.
Zelensky also said Ukraine's allies had increased their military support to the Ukrainian army, which is struggling to stop the advance of Russian forces in the east of their country.
"(Aid) accelerated in September. We are glad. We can feel the difference," he said.
Delays in the supply of weapons due to political divisions between allies left Ukrainian forces short of supplies early this year
Kyiv is heavily dependent on this military support.
Its army has fewer men and weapons than the Russian forces it has been fighting since Moscow launched a full-fledged invasion of Ukraine in February 2022.
Efforts to end the war have not yet proved successful.
Zelensky dismissed a peace plan put forward in spring by China and Brazil as too nebulous.
"I don't think it was a concrete plan. I don't see any specific action or stages in it, just generalised procedures," he said on Friday evening.
"Generalisations always hide something." he told reporters.
China and Brazil had promoted the idea of an international peace conference acceptable to both Russia and Ukraine, in which both sides would participate equally and all options would be on the table.
Beijing and Moscow have close ties which have strengthened since the Russian invasion of Ukraine.
The United States alleges that while China does not supply weapons to Russia directly, it helps Moscow increase domestic production of missiles, military drone and tanks.
Zelensky hopes to propose his so-called "victory plan" to end the war when he meets President Joe Biden in the United States next week.
"The plan is designed for decisions that will have to happen from October to December... We would like that very much. Then we believe that the plan will work," he had said earlier.
The Ukrainian leader also said he would meet Donald Trump probably on September 26 or 27.
Trump, who was US president between 2017 and 2021, has been very critical of the billions of dollars Washington has provided to Kyiv in aid and has claimed he can help end the war within 24 hours without ever explaining how.
Iran on Saturday meanwhile unveiled a new ballistic missile and an upgraded one-way attack drone, amid soaring regional tensions and allegations of arming Russia.
Iran stands accused by Western governments of supplying both drones and missiles to Russia for use in its war with Ukraine, a charge it has repeatedly denied.
Britain, France, Germany and the United States slapped new sanctions on Iran earlier this month, alleging that it had been providing ballistic missiles for Russia's war effort in Ukraine.
