(Reuters) - Russian troops will strike in unexpected parts of the front when they conduct their summer offensive in Ukraine and could try to advance on the northeastern city of Kharkiv, the commander of Ukraine's National Guard said on Tuesday.

Ukraine's second largest city has been pounded by missiles and drones in recent weeks, but Kyiv's forces will be prepared to thwart any assault, Oleksandr Pivnenko said.

"We are getting ready. Yes, the enemy will give us unpleasant surprises. It will operate in areas where we do not expect it. But it will not achieve its goal," he told the Ukrainian news outlet Liga.net.

Russia has been inching forward in the east, but long-delayed U.S. military assistance is finally expected to be approved this week and reach Ukraine soon, relieving critical ammunition shortages and air defences.

Ukrainian officials say they expect a Russian in late spring or summer, and that they believe Moscow wants to seize the strategically important eastern town of Chasiv Yar by May 9 when it marks Soviet Victory Day in World War Two.

Pivnenko said he foresaw "some difficulties" for Kyiv's troops, but that Russian forces would not make decisive gains.

"Perhaps they may be able to meet 10-15% of their goals. But this will not be a strategic victory."

He expected Russian troops to continue pounding Kharkiv's critical infrastructure, much of which has already been damaged or destroyed in Russian strikes, but not to capture the city.

(Reporting by Yuliia Dysa, Editing by Timothy Heritage, Tom Balmforth and Kevin Liffey)