U.S. Defence Secretary Lloyd Austin said Thursday President Joe Biden has approved additional military aid to Ukraine worth up to 675 million, an announcement that came as he gathered allies to renew their commitment to military support for the long haul.

Austin said at the start of a meeting with senior officials from allied countries at the United States' Ramstein Air Base in Germany that Biden approved the latest tranche of U.S. assistance on Wednesday.

He said that the package includes howitzers, artillery munitions, Humvees, armoured ambulances, anti-tank systems and more.

Austin said that the war is at another key moment, with Ukrainian forces beginning their counteroffensive in the south of the country. He said that now we're seeing the demonstrable success of our common efforts on the battlefield.

The face of the war is changing and so is the mission of this contact group, Austin told the meeting of the Ukraine Defence Contact Group, which was attended by NATO Secretary-General Jens Stoltenberg and Ukraine's defense minister as well as officials from allied countries.

We will work together to train Ukraine's forces for the long haul. We will work together to help integrate Ukraine's capabilities and bolster its joint operations for the long haul, he said.

We will work together to upgrade our defense industrial basis to meet Ukraine's requirements for the long haul, and we will work together for production and innovation to meet Ukraine's self-defense needs for the long haul.

We must evolve as the fight evolves, Austin said.

AP