Exclusive: United States defends Syria airstrikes in letter to U.N. chief

In a letter to U.N. Secretary-General Ban Ki-moon, U.S. Ambassador to the United Nations Samantha Power wrote, "The Syrian regime has shown that it cannot and will not confront these safe havens effectively itself."

The strikes were needed to eliminate a threat to Iraq, the United States and its allies, she wrote, citing Article 51 of the U.N. Charter, which covers an individual or collective right to self-defense against armed attack.

"States must be able to defend themselves ... when, as is the case here, the government of the state where the threat is located is unwilling or unable to prevent the use of its territory for such attacks," Power wrote in the letter obtained by Reuters.

"Accordingly, the United States has initiated necessary and proportionate military actions in Syria in order to eliminate the ongoing (Islamic State) threat to Iraq," she wrote, adding that action was taken also against al Qaeda elements in Syria known as Khorasan "to address terrorist threats that they pose to the United States and our partners and allies."

Ban circulated the letter to the U.N. Security Council, diplomats said. Under Article 51, the 15-member body must immediately be informed of any action that states take in self-defense against armed attack.

The United States and Arab allies bombed Syria for the first time on Tuesday, killing scores of Islamic State fighters and members of a separate al Qaeda-linked group, opening a new front against militants by joining Syria's three-year-old civil war.

Syria's U.N. Ambassador Bashar Ja'afari told Reuters on Tuesday that Power informed him in person of imminent U.S. and Arab airstrikes against Islamic State targets on Syrian territory on Monday hours beforehand.

Ja'afari said: "We're in close coordination with Iraq." The U.S. mission confirmed that Power had informed Ja'afari.

Iraq notified the Security Council in a letter on Saturday of its request for the United States to lead efforts to strike Islamic State strongholds because, it said, a safe haven for the militants in Syria had made its border "impossible to defend."

In the letter, Iraqi Foreign Minister Ibrahim al-Jaafari wrote that the safe haven for the radical Sunni Muslim group outside Iraq's borders was "a direct threat to the security of our people and territory." He did not identify Syria by name.

Power wrote in her letter to Ban on Tuesday that the Iraqi government asked the United States "to lead international efforts to strike (Islamic State) sites and military strongholds in Syria in order to end the continuing attacks on Iraq."

Ban told reporters on Tuesday that Islamic State militants pose a serious threat to international peace and security, echoing language that the U.N. Security Council has used in the past to greenlight military interventions.

"I'm aware that today's strikes were not carried out at the direct request of the Syrian government but I note that the government was informed beforehand," he said.

"I also note that the strikes took place in areas no longer under the effective control of that government," he added. "It is undeniable and the subject of broad international consensus that these extremist groups pose an immediate threat to international peace and security."

(Additional reporting by Louis Charbonneau; Editing by Howard Goller, Toni Reinhold)