The U.S. Coast Guard said Monday that it tracked a group of Russian naval vessels, including two submarines, as they crossed into U.S. waters off Alaska in an apparent effort to avoid sea ice, a move that is permitted under international rules and customs.

A Russian military aircraft was detected and tracked near U.S. airspace this past weekend in the fourth such incident in less than a week, according to NORAD.

NORAD said it intercepted Russian military aircraft off the coast of Alaska on Sunday, marking the third time in as many days and the fourth time in the past week.

Alaska Airlines flight attendants reported feeling ill after an unidentifiable odor was detected in a cabin, causing a diversion prior to hospitalization.

At 11 p.m. local time Thursday, Alaska Airlines Flight 810 left Kauai, Hawaii, and headed for Seattle. Shortly after the plane took off, it was diverted to Honolulu when four flight attendants became sick after an unknown odor was detected in the cabin, according to a statement emailed to USA TODAY by a spokesperson for the airline.

Honolulu EMS said that the flight attendants had shown symptoms of "nausea and disturbed coordination" from the smell, local media reported.