"We must be vigilant against Russia's covert activities on Alliance territory," Jens Stoltenberg said in Berlin alongside German Chancellor Olaf Scholz, quoted by the Spanish agency EFE. German authorities last week arrested two individuals accused of espionage and preparing sabotage on behalf of Moscow, while two Britons were charged on Tuesday with cooperating with Russian intelligence. "We fully support Germany and the United Kingdom. These espionage activities are dangerous and unacceptable, and they will not deter us from continuing to support Ukraine," Stoltenberg said. "We are closely coordinating our response to any hostile acts against NATO Allies," he said. Stoltenberg, who began a visit to Germany on Thursday with a trip to the Laage air base in the north of the country, praised Berlin's role in strengthening NATO's eastern flank. He also welcomed Germany's increase in defense spending in the wake of Russia's invasion of Ukraine in February 2022, towards the target of 2% of gross domestic product (GDP). Olaf Scholz reiterated the need to support Ukraine "for as long as it takes" to defend "the security architecture in Europe", which he said had been jeopardized by Russia's invasion. "We must all do more this year and in the coming years to do what is necessary," he said. Scholz said that German support for Ukraine now totals €28 billion, including aid already delivered and aid pledged. The chancellor also renewed his appeal to "friends in Europe" to check if their armed forces still have equipment that could be donated to Kyiv to bolster Ukraine's air defenses. The German government recently announced that it would deliver a third Patriot missile battery to Ukraine. Berlin has also launched a diplomatic initiative to convince other allies to step up their support for Ukrainian air defenses. Since it was invaded by Russia on 24 February 2022, Ukraine has relied on Western allies for weapons, although it has complained about the hesitation of some governments and the slow pace of deliveries. After a largely successful Ukrainian counteroffensive last summer, Russia has in recent weeks intensified its attacks on Ukraine, particularly targeting energy infrastructure. In addition to financial and military support, Kyiv's allies have also imposed sanctions on Russian interests in an attempt to reduce Moscow's ability to finance its war effort. Read Also: Two hospitals in Kyiv evacuated due to threat of bombing (Portuguese version)