South Korea said on Tuesday an agreement with the United States to scrap a weight limit on its warheads would help it respond to North Korea’s nuclear and missile threat after it conducted its sixth and largest nuclear test two days ago, Reuters reports.

South Korean officials believe more weapons tests by the reclusive state are possible, despite international outrage over Sunday’s nuclear test and calls for more sanctions against it.

South Korea’s Asia Business Daily, citing an unidentified source, reported that North Korea had been observed moving a rocket that appeared to be an intercontinental ballistic missile (ICBM) towards its west coast.

The rocket started moving on Monday and was spotted moving only at night to avoid surveillance, the newspaper said.

South Korea’s defense ministry, which warned on Monday that North Korea was ready to launch an ICBM at any time, said it was not able to confirm the report.

Analysts and South Korean policymakers believe North Korea may test another weapon on or around Sept. 9, when it celebrates its founding day.

North Korea’s fifth nuclear test fell on that date last year, reflecting its tendency to conduct weapons tests on significant dates.

North Korea says it needs to develop its weapons to defend itself against what it sees as U.S. aggression.

South Korea, after weeks of rising tension, is talking to the United States about deploying aircraft carriers and strategic bombers to the Korean peninsula, and has been ramping up its own defenses.

U.S. President Donald Trump and his South Korean counterpart, Moon Jae-in, agreed on Monday to scrap a warhead weight limit on South Korea’s missiles, South Korea’s presidential office said, enabling it to strike North Korea with greater force in the event of war.

The White House said Trump gave “in-principle approval” to the move.