WASHINGTON (AP) — The U.S. announced plans on Tuesday to provide an additional $625 million in military aid to Ukraine, a package that includes additional advanced rocket systems credited with helping the country’s military gain momentum in its war with Russia.

President Joe Biden provided details on the latest package—which includes four High Mobility Artillery Rocket Systems, known as HIMARS, 200 mine resistant vehicles, hundreds of thousands of rounds of artillery and mortar ammunition—in a call with Ukrainian President Volodymyr Zelenskyy. Vice President Kamala Harris joined the leaders on Tuesday’s call.

The U.S. and Ukraine leaders spoke as Russia’s upper house of parliament on Tuesday formally approved the annexation of swaths of Ukrainian territory following referendums that Ukraine and its Western allies dismissed as fraudulent.

“President Biden also affirmed the continued readiness of the United States to impose severe costs on any individual, entity, or country that provides support to Russia’s purported annexation,” the White House said in a statement.

This round of military aid marks the first time the U.S. has sent additional HIMARS to Ukraine since late July. The systems—which will bring the total number of HIMARS sent to Ukraine to 20— have become a key tool in Ukraine’s ability to strike bridges that Russia has used to supply its troops, enabling Ukrainian forces to make inroads in Russia-controlled regions.

The U.S. in recent weeks also provided funding through a separate program — the Ukraine Security Assistance Initiative — so another 18 HIMARS can be purchased through longer-term contracts. USAI funds are being used as part of the effort by the U.S. and Western allies to ensure Ukraine’s forces are trained and equipped to defend their country in the years to come. But those contracts will take several years to fulfill.

This is the first tranche of U.S. aid delivered in the new fiscal year, which began Oct. 1.

Ukraine has pressed its counteroffensive in the Kherson region since the summer, relentlessly pummeling Russian supply lines and making inroads into Russian-held areas west of the Dnieper River. Ukrainian troops have been using the HIMARS to repeatedly hit the main bridge across the Dnieper and a dam that served as a second crossing. It also has struck pontoon bridges that Russia has used to supply its troops.

Ukraine’s battlefield successes in Kherson are notable since that is one of the four areas that Russia is in the process of annexing.

Associated Press writer Lolita C. Baldor contributed reporting.