SEOUL, South Korea (AP) — North Korea launched suspected ballistic missiles toward the sea on Tuesday in apparent weapons tests, according to its neighbors, as the North heightens animosities with rival South Korea ahead of a major political meeting.

Japan’s Prime Minister's Office and Defense Ministry said North Korea fired possible ballistic missiles. South Korea’s Defense Ministry said it detected the launch of at least one unidentified projectile off North Korea's east coast. Neither country immediately provided details such as how far the North Korean weapons traveled.

Tuesday’s launch came after North Korea recently threatened retaliation over what it called South Korean surveillance drone flights across the border, one earlier in January and another in September. The South Korean government denied operating any drones during the times specified by North Korea and began probing if civilians sent them.

Analysts said North Korea’s drone accusations likely were driven by its efforts to dial up anti-South Korea sentiments ahead of the ruling Workers’ Party congress, which is expected to start in late January or February. The North could add leader Kim Jong Un’s declaration of a hostile “two-state” system on the Korean Peninsula in the party constitution during the congress, the first of its kind in five years.

Earlier this month, North Korea said it performed test flights of hypersonic missiles. Kim observed the launches and underscored the need to bolster the country’s nuclear war deterrent, according to North Korea’s state media.

North Korea in December test fired what it called long-range, strategic cruise missiles and new anti-air missiles and released photos showing the apparent construction of its first nuclear-powered submarine.

North Korea aimed to demonstrate or review its achievements on the weapons development sector ahead of the party congress, analysts said.

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Mari Yamaguchi in Tokyo contributed to this report.