WASHINGTON - The United States will provide advanced rocket systems to Ukraine to use in defense against Russian forces but not for strikes inside Russia, a White House official said on Wednesday as Washington seeks to contain escalation of the conflict.

U.S. President Joe Biden has agreed to provide Ukraine with rocket systems that can strike with precision at long-range Russian targets as part of a $700 million weapons package expected to be unveiled on Wednesday.

Jonathan Finer, deputy White House national security adviser, said the Ukrainians have been requesting the system and Washington believes it will meet their needs.

"We have asked Ukrainians for assurances that they will not use these systems to strike inside Russia. This is a defensive conflict that the Ukrainians are waging. Russian forces are on their territory," Finer said in an interview with CNN.

There are significant targets Ukrainians cannot reach with the weapons they currently have, Finer said, and the rocket system will make a big difference in the conflict in the southeastern part of the country, where Russian forces are currently focused.

A senior administration official said on Tuesday Ukraine gave assurances they will not use the long-range missiles to strike inside Russia.

The package also ammunition, counter fire radars, a number of air surveillance radars, additional Javelin anti-tank missiles, as well as anti-armor weapons, officials said.

Ukrainian officials have been asking allies for longer-range missile systems that can fire a barrage of rockets hundreds of miles away, in the hopes of turning the tide in the war, which is in its fourth month.

A Russian official said Moscow viewed the development "extremely negatively." Finer, however, said Biden had told Russian President Vladimir Putin directly what the consequences of any Ukraine invasion would be.

"We are doing exactly what we said we would do," he said. "Russia has brought this on itself by launching an invasion into a sovereign country from its territory."

Thousands of people have been killed in Ukraine and millions more displaced since the Russian invasion on Feb. 24.

As the United States and its allies provide Ukraine with increasingly sophisticated arms, Washington has held discussions with Kyiv about the danger of escalation if it strikes deep inside Russia, U.S. and diplomatic officials have told Reuters.

U.S. intelligence has also warned about growing risks.

Biden on Tuesday told reporters that "we're not going to send to Ukraine rocket systems that strike into Russia."

(Reporting by Doina Chiacu; Editing by Frank Jack Daniel)