Spain on Monday pledged one billion euros in military aid to Ukraine as Prime Minister Pedro Sanchez and Ukraine's President Volodymyr Zelensky signed a security deal in Madrid.

The deal "includes a commitment for one billion euros in military aid for 2024," Sanchez told a joint news conference

"It will allow Ukraine to boost its capabilities including its essential air defence systems to protect its civilians, cities and infrastructure which are still suffering indiscriminate attacks as seen this weekend in Kharkiv," he said, referring to a Russian strike on the northeastern city that killed at least 16 people.

Zelensky's visit comes as Ukraine has been battling a Russian ground offensive in the Kharkiv region which began on May 10 in Moscow's biggest territorial advance in 18 months.

With the Russian assault now in its third year, Ukraine has been pleading for more weapons for its outgunned and outnumbered troops, notably seeking help to address its lack of air defence systems.

Sanchez said Spain had already pledged to supply Patriot missiles, but what Zelensky needed from Ukraine's allies was "the systems to launch these missiles".

"That's what he working on with different allies to see exactly how many we can send to guarantee this aerial security."

Spain would also send "another batch of Leopard tanks and above all ammunition," Sanchez said, pledging to keep working with Kyiv "to understand how else -- and with what other alternative systems -- we can help ensure Ukraine's air security."

 For defensive purposes 

Zelensky has already signed bilateral security agreements with several countries including France, Germany and the UK.

Sanchez said the security agreement would cover a range of a different issues, ranging from "military, humanitarian and financial support, to collaboration between Spanish and Ukrainian defence industries, as well as help with reconstruction and de-mining among other things".

Last month, Spain pledged to send an unspecified number of Patriot air defence missile systems to Ukraine; it has previously sent 10 Leopard tanks.

Until now, Madrid has only provided limited military aid to Kyiv.

According to the Kiel Institute -- which tracks weapons pledged and delivered to Ukraine since the Russian invasion -- Spain has so far committed 330 million euros in military aid, making it a small contributor on a European level.

By comparison, Berlin, Paris and Rome have committed 18.61 billion, 5.65 billion and 1.0 billion euros respectively, while London's contribution stands at 9.22 billion, the figures show.

Following talks with Sanchez, Zelensky met King Felipe VI for talks at the palace and then lunch, after which the monarch said "more than 4,300 Ukrainian soldiers" had already received training in Spain.

Spain's military support was purely for defensive purposes, the king said, indicating it was "based on the rejection of the use of armed force in an international context" -- effectively a ban on firing such arms into Russian territory.

Washington and other allies have also imposed a similar ban.