President Obama has taken the formal step of notifying Congress that he has deployed troops "equipped for combat" to Libya and Yemen to defend U.S. citizens and property, pursuant to the War Powers Resolution.

"Although these security forces are equipped for combat, these movements have been undertaken solely for the purpose of protecting American citizens and property," the president wrote in a letter to Congress. "These security forces will remain in Libya and in Yemen until the security situation becomes such that they are no longer needed."

A security force from the U.S. Africa Command deployed to Libya Wednesday to support security of U.S. personnel after the killing of four Americans in an attack on the U.S. embassy in Benghazi. An additional security force arrived in Yemen Thursday after the assault on the U.S. Embassy in Sana'a.

"These actions have been directed consistent with my responsibility to protect U.S. citizens both at home and abroad, and in furtherance of U.S. national security and foreign policy interests, pursuant to my constitutional authority to conduct U.S. foreign relations and as Commander in Chief and Chief Executive," the president wrote. "I am providing this report as part of my efforts to keep the Congress fully informed, consistent with the War Powers Resolution. I appreciate the support of the Congress in these actions."

Consistent with the War Powers Resolution, the president has to notify Congress when he dispatches combat-equipped troops to a foreign country.

This situation differs from the U.S. involvement in Libya last year, when the president was criticized for not notifying Congress.

No combat-equipped troops were sent to a foreign country in that instance, whereas these are now boots on the ground.

ABC News' Jake Tapper contributed to this report.