BEIRUT, Lebanon (AP)—Iranian-backed Hezbollah extremists clashed Sunday with Shiite militiamen searching for a kidnapped U.S. Marine and declared support for his abductors.

A Hezbollah leader said he believed Lt. Col. William R. Higgins had been smuggled out of south Lebanon.

“We declare solidarity with, and full support for, the strugglers against America who confront the plots of the great Satan,” said a statement from Hezbollah, or Party of God. “The demands of the Organization of the Oppressed on Earth are just.”

The Organization of the Oppressed on Earth on Friday claimed responsibility for Higgins’ kidnapping, charging he was a CIA spy. U.S. and U.N. officials denied the charge.

Higgins, a decorated Vietnam veteran and a one-time military assistant to former U.S. Defense Secretary Caspar Weinberger, heads a 76-man observer group attached to a U.N. peacekeeping force in south Lebanon. He was kidnapped on Wednesday near the ancient port city of Tyre.

Hezbollah is believed to be the umbrella organization for pro-Iranian groups holding foreign hostages in Lebanon.

Police said Hezbollah and Justice Minister Nabih Berri’s mainstream Shiite Amal militia clashed in a brief firefight in the southeastern Lebanese village of Ein el-Tineh. No casualties were reported.

Hezbollah militiamen opened machine-gun fire on an Amal patrol near the village in the western sector of the Bekaa valley and the patrol fired back rocket-propelled grenades, said a police spokesman, who spoke on condition of anonymity according to regulations.

When the 30-minute clash ended and the Amal patrol left, Hezbollah gunners pounded Israel’s self-designated security zone in south Lebanon with mortars, the spokesman said.

He said Israel retaliated by shelling 13 southern Shiite villages for three hours. Four civilians were wounded, police said.

Police said the clash was caused by the ongoing search for Higgins and the recent arrest of Hezbollah members linked to the kidnapping.

Ein el-Tineh, a Hezbollah stronghold, is 31 miles east of Tyre, where Hezbollah claims Amal has arrested more than 150 of its members in connection with Higgins’ abduction. Amal spokesmen say only 40 fundamentalists have been detained.

The abduction prompted the U.N.‘s Interim Forces In Lebanon to withdraw 20 observers from Higgin’s unit to its headquarters in Naqoura, near the Israel-Lebanon border, according to Timor Goksel, spokesman for the UNIFIL.

Goksel said the observers were withdrawn both for security concerns and to protest Higgins’ abduction. The rest of the observer group remained Sunday in positions overlooking Beirut’s green line, which divides the city into Moslem and Christian sectors, he said.

Goksel declined to comment on reports that U.N. troops had abandoned checkpoints around Tyre.

Ten UNIFIL troops were withdrawn Thursday to Naqoura from an area close to an Amal checkpoint on the Qassmieh highway bridge north of the city. But UNIFIL troops did not withdraw from any of their own checkpoints south and east of Tyre.

UNIFIL units and Amal militiamen, aided by helicopters and dogs, continued to search for Higgins Sunday in olive and citrus groves and cave-lined valleys southeast of Tyre.

Berri has called Higgins’ abduction a threat to the security of the predominantly Shiite population of south Lebanon. He said Amal was bent on defending the U.N. peacekeeping force irrespective of the nationality of its officers.

Sheik Abdul-Karim Obeid, a Hezbollah leader in south Lebanon, was quoted by Beirut radio stations Sunday as saying he believes the kidnappers have managed to smuggle Higgins out of the south.

As a condition of Higgins’ release, the Oppressed on Earth has demanded that Israel withdraw from the security zone it carved out in south Lebanon when the bulk of its occupation army withdrew from Lebanon in 1985, ending a three-year invasion.