"This is first time since February 2022 when such a [concentration] of Ukrainian troops with western artillery, with western HIMARS (High Mobility Artillery Rocket System) and western missiles was collected together for this counterattack,” Poroshenko added.
The counteroffensive comes as Russia's war in Ukraine has passed its six-month mark, with US assessments indicating that Russia has been able to deploy fewer units to the frontlines than initially thought, according to a senior US official.
On Monday morning, Ukraine indicated that actions were underway.
"Ukrainian armed forces have started the offensive actions in several directions on the South front towards liberating the occupied territories," Natalia Humeniuk, a spokesperson for Ukraine's Operational Command South, told CNN.
"All the details will be available after the operation is fulfilled," she added.
International Atomic Energy Agency (IAEA) inspectors are expected to go to Zaporizhzhia nuclear power plant in southeast Ukraine sometime this week amid renewed shelling at the Russian-held facility and mounting fears over a potential nuclear accident -- which has seen Ukrainian officials make iodine pills available to residents.
This comes as Ukraine forces prepare for a counteroffensive in the south, according to United States officials.
"Shaping" operations begin: Ukraine's forces are preparing the battlefield for a significant Ukrainian counteroffensive, two senior US officials told CNN. Shaping operations are standard military practice prior to an offensive and involve striking weapons systems, command and control, ammunition depots and other targets to prepare the battlefield for planned advances. According to the officials, the US believes the much-anticipated counteroffensive will include a combination of air and ground operations.
IAEA inspectors heading in: A team from the IAEA -- the UN nuclear watchdog -- is on its way to Zaporizhzhia nuclear power plant and will be there "later this week," IAEA Chief Rafael Mariano Grossi tweeted Monday. The mission will assess damage to the plant's facilities, evaluate the working conditions of the staff and perform urgent safeguard activities. Ukraine's Foreign Minister Dmytro Kuleba said the international community should demand Russia's withdrawal from the plant so as to ensure nuclear security. The Kremlin welcomed the news of the visit, saying the IAEA mission will enter Zaporizhzhia nuclear plant from the Ukrainian side, but Russia will ensure its safety on the territory occupied by the Russian army.
Renewed shelling: The city of Orikhiv in the Zaporizhzhia region suffered more than 200 attacks in a six-hour time span, say Ukrainian officials. Shelling also occurred in the Russian-controlled city of Enerhodar, close to the nuclear plant, on Sunday night, Russian and Ukrainian officials said -- with each side blaming the other for the attacks.