The United States will send Ukraine advanced rocket systems and munitions as part of a new $700 million package of military equipment intended to help the Ukrainians fight back against the Russian invasion of their country, President Biden and White House officials said on Tuesday.

Mr. Biden announced his decision to provide the rocket systems, which can precisely target an enemy from almost 50 miles away, in an Op-Ed published online Tuesday evening by The New York Times. He said the delivery of the advanced weapons would enable Ukraine to “fight on the battlefield and be in the strongest possible position at the negotiating table.”

But a senior administration official said later that the weapons system — the most advanced provided to the Ukrainians to date — was promised only after direct assurances by Ukraine’s leaders that they would not use it against targets within Russian territory.

As the war has dragged on, the Biden administration has progressively widened the array of weaponry it has provided to the Ukrainians, and the latest package will also include Javelin antitank missiles, artillery rounds, helicopters and tactical vehicles. But top administration officials have been concerned about provoking a broader war with President Vladimir V. Putin of Russia by providing equipment that could allow Ukraine to strike deep inside his country.

That has proved to be a tricky line to walk for the president and his advisers since Mr. Putin sent his troops into Ukraine nearly 100 days ago.

In his article on Tuesday, Mr. Biden described his administration’s resolve to support Ukraine in its attempts to repel Russian invaders. But Mr. Biden also offered specific assurances for Mr. Putin that the United States does not intend to provoke a wider conflict or the use of weapons of mass destruction.