KYIV: Ukraine’s President Volodymyr Zelensky sacked the head of the country’s domestic security service and state prosecutor, citing hundreds of cases of alleged treason and collaboration with Russia, as Moscow appeared set to step up military operations. Zelensky said more than 60 officials from the SBU security service and prosecutor’s office were working against Ukraine in Russian-occupied territories, and 651 treason and collaboration cases had been opened against law enforcement officials. The sackings on Sunday of Ivan Bakanov, head of the security service, and Prosecutor General Iryna Venediktova, who led efforts to prosecute Russian war crimes, and the sheer number of treason cases reveal the huge challenge of Russian infiltration as Kyiv battles Moscow in what it says is a fight for survival. “Such an array of crimes against the foundations of the national security of the state…pose very serious questions to the relevant leaders,” Zelensky said. “Each of these questions will receive a proper answer. In his nightly speech to the nation, Zelenskiy noted the recent arrest on suspicion of treason of the SBU’s former head overseeing the region of Crimea, the peninsula annexed by Russia in 2014 that Kyiv and the West still view as Ukrainian land. Zelensky said he had fired the top security official at the start of the invasion, a decision he said had now been shown to be justified. “Sufficient evidence has been collected to report this person on suspicion of treason. All his criminal activities are documented,” he said. 3,000 cruise missiles After failing to capture the capital Kyiv early in the invasion, Russian forces using a campaign of devastating bombing now control large swaths of Ukraine’s south and east, where pro-Russian separatists already control territory. Zelensky said Russia had used more than 3,000 cruise missiles to date and it was “impossible to count” the number of artillery and other strikes so far. But Western deliveries of long-range arms are beginning to help Ukraine on the battlefield, with Kyiv citing a string of successful strikes carried out on 30 Russian logistics and ammunitions hubs, using several multiple launch rocket systems recently supplied by the West. The strikes are causing havoc with Russian supply lines and have significantly reduced Russia’s offensive capability, according to Ukraine’s defense ministry. Ukrainian officials say the new U.S.-made High Mobility Artillery Rocket Systems (HIMARS) they began receiving last month allows them to reach targets in Crimea, which was annexed by Russia in 2014, and other areas occupied by Russia. “Good morning from HIMARS,” Andriy Yermak, chief of staff to Ukraine’s president, wrote on Telegram on Sunday alongside a video showing a large explosion which he said was another destroyed Russian ammunition depot in southern Ukraine. Russia intensifies operations Russian Defence Minister Sergei Shoigu on Saturday ordered military units to intensify operations to prevent Ukrainian strikes on areas held by Russia, according to a statement from the ministry. Ukrainian military intelligence later reported shelling along the entire frontline and what it said was preparation for the next stage of the Russian offensive. The Ukrainian military said Russia appeared to be regrouping units for an offensive toward Sloviansk, a symbolically important city held by Ukraine in the eastern region of Donetsk. The British defense ministry said on Sunday that Russia was also reinforcing defenses across areas it occupies in southern Ukraine after pressure from Ukrainian forces and pledges from Ukrainian leaders to drive Russia out. Russian President Vladimir Putin launched his invasion on Feb. 24 calling it a “special military operation” to demilitarise its neighbor and rid it of dangerous nationalists. Kyiv and the West say it was an imperialist land grab and attempt to reconquer a country that broke free of Moscow’s rule with the break-up of the Soviet Union in 1991. The biggest conflict in Europe since World War Two has killed more than 5,000 people, forced more than 6 million to flee Ukraine, and left 8 million internally displaced, says the United Nations. Ukraine and the West say Russian forces are targeting civilians and have been involved in war crimes, charges Moscow rejects. Russia is preparing for the next stage of its offensive in Ukraine, a Ukrainian military official said, after Moscow said its forces would step up military operations in “all operational areas”.