BEIRUT — Lebanon's Army said it will respond immediately to any further cross-border attacks by the Syrian military after a helicopter gunship attacked the eastern town of Arsal on Wednesday.

President Michel Sleiman called the attack "a violation of Lebanon's sovereignty" and said the country has the right to take steps to defend itself and to "submit a complaint" to the United Nations and the Arab League.

"Army units deployed in the [Arsal] area took the necessary defensive measures to respond immediately to any similar violations," an army statement said in a rare warning against the regime of Syrian President Bashar al-Assad.

Earlier on Wednesday, a helicopter raided Arsal, where a majority of residents support the anti-Assad revolt, for the first time in the nearly 27-month conflict.

At 1:30 p.m., "a Syrian helicopter gunship crossed the border . . . and launched two rockets from a distance at the (Arsal) town center, injuring one person and causing material damage," the army said.

Sleiman, meanwhile, in a statement said "the repeated strikes on Arsal by Syrian helicopter gunships constitute a violation of Lebanon's sovereignty and its territorial integrity."

The strikes violate "the conventions that regulate relations between the two countries, as well as international treaties, at a time when the Lebanese state is trying to maintain stability and social peace in Lebanon," he added.

The president called on Syria not to repeat the strikes, and said "Lebanon has the right to take the necessary steps to defend its sovereignty . . . including the right to submit a complaint to the Arab League and the United Nations."

Damascus dominated Lebanon politically and military for 30 years until 2005, and continues to exert significant influence through its allies including the Shiite Hezbollah movement in the Mediterranean country.

Lebanon's poorly equipped army coordinates closely with the Syrian military.

Arsal is sensitive because it is just 12 kilometers (7.5 miles) from the border with Syria. Experts say it has been used as a conduit for weapons and rebels to enter Syria, while it has also served as a refuge for people fleeing the conflict into Lebanon.

Dozens of people wounded in fighting in the key town of Qusair — most of them rebels — flocked to Arsal for treatment last week as the Syrian army and Hezbollah overran the former insurgent bastion.