Ukrainian President Volodymyr Zelenskyy has said his military needs more time to prepare for its highly anticipated counter-offensive against Russian forces.
In an interview with the BBC on Thursday, he said the operation could go ahead, but that Ukraine would “lose a lot of people”.
Mr Zelenskyy said: "With [what we have] we can go forward and be successful. But we'd lose a lot of people. I think that's unacceptable. So we need to wait. We still need a bit more time."
The Ukrainian military has have been training a new contingent of forces and stockpiling western-supplied munitions and hardware that analysts say will be key to reclaiming territory captured by Russia.
The timing of Kyiv's effort to claw back ground in the eastern Donetsk and Lugansk regions, as well as the Kherson and Zaporizhzhia regions, remains a question.
Ukrainian Defence Minister Oleksiy Reznikov said late last month that Kyiv's preparations were "coming to an end" and his forces were ready "in a global sense".
A senior Ukrainian military official said this week that Russian forces had dropped back from some areas near Bakhmut after limited counter attacks by Kyiv's forces around the eastern city.
Earlier this week, the United States announced a new $1.2 billion security assistance package for Ukraine to boost the country's air defences and provide it with additional artillery ammunition.
The latest assistance must be procured from the defence industry or partners, which will avoid depleting US stocks, but mean the assistance will take longer to reach Kyiv.
The package underscores the continued US support for Ukraine "by committing critical near-term capabilities, such as air defence systems and munitions, while also building the capacity of Ukraine's armed forces to defend its territory and deter Russian aggression over the long term", the Defence Department said in a statement.
The package features unspecified air defence systems and munitions as well as equipment to integrate western systems with Ukraine's existing gear, which is mainly of Soviet vintage.
Pentagon spokesman Brig Gen Pat Ryder said on Tuesday that the specific air defence systems have not yet been selected, saying the announcement represents "the beginning of a contracting process to provide additional priority capabilities to Ukraine".
US Secretary of State Antony Blinken said at a news conference alongside his British counterpart on Tuesday that Ukraine has what it takes to "continue to be successful in regaining territory that was seized by force by Russia over the last 14 months".