Zelensky will attend the summit, which marks the 75th anniversary of the trans-Atlantic alliance and which will bring together leaders of countries that have provided Kyiv with tens of billions of dollars in military aid to help it counter Russia's invasion.

With Ukraine unlikely to receive the invitation to join NATO that it is seeking, new air defenses are the most concrete assistance it is likely to get at the summit.

Below, AFP examines key questions about Ukraine's air defense needs and how they could be addressed.

- What systems does Ukraine want? -

Zelensky has for months said his country does not have enough air defense systems and has requested at least seven more Patriot batteries in addition to those already donated by the United States, Germany and the Netherlands.

Over the weekend, the Ukrainian leader praised air defense donations but said "more concrete decisions" are needed "to protect all our cities and villages, and to truly overcome Russian terror."

"Next week, we will work with our partners for such decisions -- preparations are already underway," he said.

- Why does Ukraine need them?

Russia has exploited gaps in Ukraine's air defenses to carry out devastating strikes on civilians and infrastructure, as well as to pummel Kyiv's troops on the front lines.

Highlighting the threat, Ukrainian officials said more than 30 people were killed on Monday by a wave of dozens of missiles that hit cities across the country and ripped through a children's hospital in Kyiv.

Russia has meanwhile claimed recent attacks on three Ukrainian air bases, raising questions over how Kyiv will protect a fleet of F-16 fighters due to arrive in the country later this year.

And Ukraine pointed to its lack of air superiority as a major factor limiting its army's ability to advance on the battlefield following Kyiv's lackluster 2023 counter-offensive.

Ukraine's international supporters have sought to cobble together multi-layer air defenses for the country consisting of low-, medium- and high-altitude systems that can protect against a variety of threats.

But doing so from a mix of different new and older Western and Soviet-era systems in the midst of an active conflict has proven to be a significant challenge, and shortfalls remain.

- What will Kiv receive? -

The United States is reportedly considering donating another Patriot battery to Kyiv, which sees them as particularly valuable because it is one of the only systems capable of downing Russia's most advanced missiles.

US President Joe Biden on Monday promised action to boost Ukraine's defenses in a statement that described Moscow's missile strikes that day as a "horrific reminder of Russia's brutality."

"Together with our allies, we will be announcing new measures to strengthen Ukraine's air defenses to help protect their cities and civilians from Russian strikes," Biden said in a statement, without providing specifics.

Washington is also in talks about potentially transferring up to eight Patriot batteries from Israel to Ukraine, US media has reported.

And the Netherlands is spearheading an effort to construct a Patriot missile system out of different components from the stockpiles of various countries.

Germany and Romania have already responded to Zelensky's pleas for Patriots by pledging one additional system each, while Italy has said it will donate an advanced SAMP/T air defense system.