SEATTLE - A group of protesters gathered at the Port of Seattle on Tuesday seeking to block workers attempting to reach a Royal Dutch Shell drilling rig that could depart this week to resume fossil fuel exploration in the Arctic. Over the past month, activists have staged demonstrations against the oil company’s plans to drill for oil in the Arctic, including on May 16 when hundreds of protesters in kayaks and small boats fanned out on a Seattle bay. Several dozen protesters gathered early on Tuesday to block entrances to Terminal 5 at the Port of Seattle where the rig is being outfitted for its trip north to the Chukchi Sea off Alaska. Shell did not immediately respond to an email seeking comment on the protest. There have been no arrests, Seattle police said. Environmental groups say drilling in the icy Arctic region, where weather changes rapidly, could lead to a catastrophic spill. They also say drilling would threaten the Arctic’s vast layer of sea ice that helps regulate the global temperature and which they say has already been disappearing as a result of global warming. The activist group ShellNo has helped organize a series of “rapid response” protests as Shell readies its drilling rig in Seattle, a city known for its support for environmental causes. The group said on its website on Tuesday that the rig, the Polar Pioneer, could begin moving north as early as Wednesday. Neither Shell nor shipping company Foss Maritime has commented publicly on the schedule. Activists say they want to get boats on the water as soon as they learn the rig is leaving the terminal. A mandatory safety zone enforced by the U.S. Coast Guard will keep watercraft at least 100 yards away from the rig. The zone will expand to 500 yards when it hits the broader Puget Sound on its way to Alaska. On Monday, Seattle police dismantled but did not seize a large tent used by demonstrators to organize the launch of a planned rig-stopping flotilla, law-enforcement officials and activists said. Late last month, Alaska Governor Bill Walker toured the rig, saying Shell’s resumption of drilling in the Arctic will bring jobs and money to his state.