WASHINGTON — In an early-morning tweet Wednesday, President Trump claimed undue credit for revamping the nation’s nuclear arsenal, wrongly suggested tremendous progress had been made since he took office, and misrepresented the sequence and scope of his executive actions.

“My first order as President was to renovate and modernize our nuclear arsenal. It is now far stronger and more powerful than ever before,” he wrote on Twitter, after exchanging escalating statements with North Korea this week.

Efforts to modernize the nation’s nuclear arsenal — including intercontinental ballistic missiles, submarine-launched ballistic missiles, strategic bombers, warheads and infrastructure — began under President Barack Obama, and will span three decades at a cost of about a trillion dollars.

The size and strength of the United States’ nuclear arsenal remains virtually unchanged since Mr. Trump took office. Since January, when the United States had a stockpile of 4,018 warheads, “a small number of warheads are thought to have been retired for an estimated 4,000 remaining in the stockpile,” according to the Federation of Atomic Scientists. The Arms Control Association, a Washington-based group, has reported no change in its estimate since January.