The upgrade involves Russia's Iskander-M and Kinzhal missiles, with a range of up to 500km and 480km respectively.
Ukrainian and Western officials said the missiles flew along a standard flight path before suddenly landing, making it difficult for patriot systems to intercept.
A former Ukrainian official described it as a "turning point for Russia".
Ukraine's missile interception rate has fallen sharply in recent months, from 37% in August to just 6% in September, according to data from the Ukrainian Air Force.
The source said that earlier this year, Russia attacked at least four drone manufacturing facilities near Kiev, causing great damage.
One of these targets was Turkey's Bayraktar drone factory, which was attacked on August 28.
In the attack, the Russian missile overtook air defense systems and also damaged nearby offices of the EU and British Council delegations.
The report by the US Special Inspector General of the US Defense Intelligence Service for the period from April 1 to June 30 stated that the Ukrainian armed forces "had difficulty in continuously using patriot air defense systems to counter Russian ballistic missiles due to recent tactical improvements by Russia, including improvements allowing missiles to change trajectory and mobile aerial vehicles instead of flying in traditional ballistic trajectory".
The patriot air defense system is the only system in Ukraine's arsenal capable of firing down Russian ballistic missiles.
This is an important element of Ukraine's multi-layered defense system to protect urban areas, including the capital Kiev, from large-scale attacks.
The information was released after a report showed that the US provided Ukraine with intelligence to carry out long-range strikes on energy infrastructure targets inside Russia.
Washington is also considering whether to send missiles to Kiev for use in such attacks. Among them is the Tomahawk cruise missile, with a range of 2,500km.
The provision of intelligence and missile equipment could make it easier for Ukraine to attack infrastructure such as refineries, oil pipelines and power plants, affecting Russia's revenue.
