WASHINGTON, Aug 14 (Reuters) - The United States said on Monday it will send Ukraine new security assistance valued at $200 million, including air defense munitions, artillery rounds, and additional mine-clearing equipment.

The assistance will also include anti-armor capabilities, U.S. Secretary of State Antony Blinken said in a statement.

Two U.S. officials told Reuters last Monday that Washington would begin to dole out $6.2 billion of funds discovered after a Pentagon accounting error that overvalued billions of dollars of Ukraine aid.

In May, the Pentagon announced it had mistakenly assigned a higher-than-warranted value to the U.S. weaponry shipped to Kyiv when staff used "replacement value" instead of "depreciated value" to tabulate the billions' worth of ammunition, missiles and other equipment sent to Ukraine.

Ukraine needs weaponry that can be shipped from U.S. stocks in a matter of days or weeks so it can continue to repel Russia's invasion. The accounting error works to Kyiv's benefit because more equipment can be sent.

"I want to thank the United States today for the new package. Munitions for Patriots, for HIMARS, artillery, Javelins and more. These are much-needed things," Ukraine's President Volodymyr Zelenskiy said in his evening address on Monday.

"There will be even more work soon with our partners for the sake of defence," he added.

Beginning to use these discovered funds is significant because they represent the last of the previously congressionally authorized $25.5 billion worth of Presidential Drawdown Authority (PDA) the administration can utilize to ship weapons from U.S. stocks in the event of an emergency, the U.S. officials said.

Washington is currently working on a supplemental budget request to continue to aid Kyiv, the U.S. officials said.

Monday's announcement of $200 million would be the first tranche of a $6.2 billion windfall of previously authorized Presidential Drawdown Authority (PDA), the officials said.