Russia has struggled to take out Ukraine's US-supplied HIMARS rocket launchers, a defence expert has claimed.

Ukrainian defence forces have been supplied with 20 of the High Mobility Artillery Rocket Systems, which have been hailed as playing a crucial part in the fight against Russia's stalled invasion.

HIMARS have a longer range and are more precise than Ukraine's Soviet-era artillery, allowing Ukrainian forces to hit Russian targets that were previously unreachable.

The technology has the ability to hit a target from 52 miles away within a radius of 16ft. Critically, they are also wheel-mounted, which makes them significantly more agile on the battlefield.

On Monday, the Ukrainians began a significant move to retake southern areas of Ukraine that have been occupied by Russia since the beginning of the invasion.

Read more: Ukrainian military activity suggests Kherson counteroffensive is underway

The southern city of Kherson had a pre-war population of 280,000, was the first major Ukrainian city to fall in February, and has been used as a base for Russian aircraft to operate out of.

In recent months, Kyiv has been shelling nearby towns, villages, and bridges in an effort to soften up Russia positions, and the donated HIMARS have been instrumental in gaining ground.

Justin Bronk, a senior research fellow at the Royal United Services Institute defence think tank, said of the weapons: "They're very, very accurate, they're very long range and can be reloaded and moved quickly.

"The Russians haven't had any success in taking out any of the 20 HIMARS launchers that have been sent, and because of their long range and the precision that they can bring they've been instrumental in allowing the Ukrainians to particularly destroy Russian bridgeheads," he told the BBC.

Bronk said the Russians would be "vulnerable" if bridges surrounding Kherson continue to be hit, and could impact what weapons Putin's troops can bring in to defend themselves.

Read more: What's at stake for Ukraine in the Battle of Kherson

He added the precision strikes have been "really starving Russian firepower on the front lines".

Bronk said the Ukrainians have been changing their communications on the offensive in recent weeks, in an effort to keep Moscow guessing their next move.

He said: "The Ukrainian government has been effectively telegraphing that they've been planning a major offensive to retake large areas of the south, particularly around Kherson, for several months now although interestingly in the past couple of weeks, they've started to pour cold water on the idea of a full offensive.

"It's worth remembering that Ukraine has been extremely capable in shaping the information environment around this war since February so clearly, they're trying to keep the Russians guessing."

Read more: U.S. agrees to send Ukraine more HIMARS launchers, weaponry that is taking a toll on Russian forces

Ukrainian President Volodymyr Zelenskyy has previously hailed the impact of the HIMARS weapons.

"The word "HIMARS" has become almost synonymous with the word "justice" for our country, and the Ukrainian defense forces will do everything to ensure that the occupiers experience more and more painful losses every week thanks to these very effective systems;" he said earlier this month.

Zelenskyy also cautioned on Monday that people will not “hear specifics” about Ukrainian military plans “from any truly responsible person,” adding “because this is war.”

"If they want to survive, it's time for the Russian military to run away. Go home," Zelenskyysaid in a late night address.

"Ukraine is taking back its own (land)."

In response, Kremlin spokesperson Dmitry Peskov said on Tuesday that Russia was methodically pressing on with its plans in Ukraine, adding: "All of our goals will be reached."

Speaking to Yahoo News on condition of anonymity, a senior official in the Ukrainian military said the offensive was indeed underway. “Obvious progress would be hard to deny,” the official said.