SEOUL, South Korea (AP) — North Korea on Thursday fired two unidentified projectiles into the sea, South Korea’s military said, three days after the North said its troops conducted artillery drills near its disputed sea boundary with South Korea.

The launches were an apparent attempt by North Korea to pressure the United States to make concessions in their stalemated nuclear diplomacy.

Seoul’s Joint Chiefs of Staff said in a statement that the projectiles were launched toward the North’s eastern waters after lifting off from the country’s northeastern South Hamgyong province.

It said South Korea’s military is monitoring possible additional launches by North Korea. It gave no further details, such as what kind of projectiles were launched and where they landed.

In the past, such reports by South Korea about North Korean launches have usually turned out to be test launches of missiles, artillery pieces and other weapons. Late last month, North Korea conducted what it called a test-firing of a new “super-large” multiple rocket launcher, a day after South Korea’s military said the North fired two projectiles into its eastern waters.

On Monday, North Korea said its leader, Kim Jong Un, visited a front-line islet and ordered artillery troops there to practice firing near the sea boundary, the scene of several bloody naval clashes between the Koreas in past years. South Korea immediately protested against the drills, saying they violated an agreement last year aimed at lowering military animosity.

In recent weeks, North Korea has been stepping up pressure on the U.S. to meet a year-end deadline set by the North to offer a new initiative to salvage the nuclear diplomacy. Some experts say North Korea may resume testing long-range missiles and nuclear devices if the United States fails to meet the deadline.

The nuclear negotiations broke down in February when U.S. President Donald Trump rejected North Korean leader Kim Jong Un’s demands for major sanctions relief in return for partial disarmament.