Iran has announced it has shot down a U.S. Navy drone, claiming it entered Iranian airspace. Unnamed U.S. officials have confirmed a drone was shot down, but claimed it was in international territory. The head of Iran’s Islamic Revolutionary Guard, Major General Hossein Salami, said the incident should send a “clear message to America” not to cross Iran’s border.

The incident comes as tension continues to escalate between the two nations. On Tuesday, the United States announced it was sending 1,000 more troops to the region. Last week, the United States blamed Iran for attacking two oil tankers in the Gulf of Oman, despite a lack of any confirmed evidence. Iran has denied the attacks and has repeatedly said it is not seeking war with the U.S.

The U.S. Navy said Wednesday that fragments from a mine that allegedly struck a Japanese-owned tanker last week bear a “strong resemblance” to an Iranian mine; however, the president of the Japanese company has said the vessel was not attacked by mines but two flying objects. The U.N. and other international actors have called for restraint and a de-escalation of tensions.

Meanwhile, Secretary of State Mike Pompeo and other top Trump officials have reportedly been linking Iran to al-Qaeda and the Taliban during closed-door briefings with lawmakers, in what Democrats fear could be part of a plan to invoke the 2001 Authorization for the Use of Military Force to attack Iran.