WASHINGTON — The Pentagon on Sunday accused Iran of attempting to shoot down a U.S. Reaper drone on Thursday as the unmanned surveillance aircraft was flying over one of two crippled tankers in the Gulf of Oman.

U.S. military officials for the first time also linked Iran to a separate missile attack in Yemen on June 6 that hit another Reaper drone and forced it to crash.

The Pentagon released no video or other evidence of Iran’s involvement, and did not explain why it waited so many days before announcing the attacks, which caused no injuries.

But the decision to publicly blame Iran for them increased chances that President Donald Trump will boost U.S. forces in the Middle East or take other steps to intensify what the White House calls a “maximum pressure” campaign against Tehran.

Lt. Col. Earl Brown, a spokesman for U.S. Central Command, said a U.S. intelligence assessment had concluded that “a modified Iranian SA-7 surface-to-air missile attempted to shoot down a U.S. MQ-9 (drone) over the Gulf of Oman to disrupt surveillance” of the crippled tanker.

The Russian-designed, shoulder-fired, anti-aircraft missile missed by about a kilometer, or more than half a mile, Brown said.

Tensions flared last week after the Trump administration publicly blamed Iran for what it said were coordinated attacks on a pair of fuel tankers, owned by companies in Japan and Norway, in international waters.

Both ships suffered still-unexplained explosions shortly after dawn Wednesday and caught fire, forcing the crews to evacuate. Iran denied any role.

In the second incident, Brown said a U.S. MQ-9 Reaper was shot down over Yemen a week earlier “by what we assess to be a Houthi SA-6 surface-to-air missile.”

The president and his national security advisers are weighing “a full range of options,” including military moves, Secretary of State Michael R. Pompeo said on “Fox News Sunday.” “We are confident that we can take a set of actions that can restore deterrence.”