CAIRO – A U.S.-military-dominated peacekeeping force of 1,650 troops in Egypt’s Sinai Peninsula is finding itself caught between restive Bedouin tribesmen and an escalating Egyptian army offensive against insurgents.

At least one of the extremist groups operating in the Sinai has called for the expulsion of U.S. troops from the desert peninsula, raising the prospect that a military task force created three decades ago as a buffer between Egypt and Israel could become a target as tensions increase.

“We’re now confronted by a population that was once passive and peaceful and has now turned belligerent,” said Agustin Espinosa, the Uruguayan ambassador in Cairo, whose country has the fourth-largest contingent in the little-known Multinational Force and Observers. “For a force that has not been used to these type of external pressures and that is not configured as a strike force, this has created a new set of challenges.”

Growing lawlessness in northern Sinai has put the force on the defensive, raising questions about whether it is equipped to fulfill a peacekeeping mission amid fighting. The task force was created three decades ago to ensure Egypt and Israel abided by the terms of a peace deal, including the demilitarization of the Sinai. Its American contingent includes 800 soldiers.

In recent months, Bedouin tribesmen in the Sinai have held up convoys of international troops, refusing to let them pass until Egyptian authorities release imprisoned relatives. The tactic has proven successful. Last March, tribesmen held one of the MFO’s main bases under siege for nearly a week, refusing to let troops leave or provisions enter. In May, 10 Fijian soldiers were held hostage for two days.

The rise of militant groups in the Sinai, which rings Israel and has been become a staging ground for cross-border attacks, has alarmed U.S. officials. The extent of the threat came into sharp focus Aug. 5, when gunmen ambushed an Egyptian checkpoint, commandeered Egyptian armored vehicles and stormed an Israeli border crossing.

In the wake of the attack, which left 16 Egyptian troops dead, U.S. officials have offered to provide expanded military assistance to Cairo. Defense Secretary Leon E. Panetta told the Associated Press in a recent interview that the Pentagon has deployed a truck-mounted tracking system that will allow U.S. troops to monitor the deployment of Egyptian forces. He said Washington has not ruled out deploying additional forces to the Sinai to augment the U.S. unit.

“We just want to make sure that we know how those forces are deployed in order to ensure that we can more effectively go after those terrorists that would try to create an incident or terrorist act,” Panetta said.

The MFO began operations in 1982, becoming the most tangible element of the 1979 peace treaty between Egypt and Israel brokered by President Jimmy Carter.

The pact ended years of brutal battles between the neighboring countries. The force was created to ensure that neither country kept a large security footprint along the border. The task was fairly straightforward for decades because Egyptian President Hosni Mubarak, a staunch U.S. ally, kept peace with Israel.

After the authoritarian leader was toppled in February 2011, residents in the Sinai torched police stations and drove security forces from vast areas of the peninsula. Migrant smuggling, organ trafficking and illicit weapon trade soared in the Sinai as the government, overwhelmed by crises in Cairo, largely abandoned the destitute region. Small cells of extremists began using the area as a staging ground for attacks on Israel.