In Switzerland, three people were picked up in the cantons of Zurich, Sankt Gallen and Lucerne, national authorities said, adding that seven further searches were also carried out.
The suspects, whose identities were not released, are accused of “participation in or support for the outlawed organisation Islamic State”.
In Germany, a man was detained in the western town of Roemerberg, federal prosecutors said.
Identified only as Aleem N., he is “strongly suspected of preparing a serious violent attack threatening the security of the state and of belonging to a foreign terrorist organisation”.
He is believed to have attempted to travel from Germany via Turkey to Syria in September 2020.
“In Syria, the suspect wanted to join the foreign terrorist organisation Islamic State, attain military training and then take part in combat or terrorist attacks,” the federal prosecutor’s office said in a statement.
However, Aleem N. was unable to reach Syria for reasons that were not immediately clear and returned to Germany.
“At the latest in April 2021 he joined Isis in Germany and carried out vast propaganda activities for the group,” prosecutors said.
His duties included “mainly translating official texts, videos and audio messages by Isis from Arabic into German and distributing them on various Telegram channels in German-speaking areas”.
“Isis considered such activities to be equivalent to taking part directly in violent jihad,” it added.
The suspect is also believed to have taken part in a telephone conversation with Isis leaders in late 2021 to “verify his reliability” before travelling to “IS zones of operation”.
However, “a further attempt” to reach Syria in January 2022 “failed again”.
Aleem N. was to appear on Tuesday before a federal judge who will decide whether to remand him in custody.
German intelligence services estimate that more than 1,150 people have travelled from Germany to Iraq and Syria since 2011 for Islamist reasons.
More than a third have since returned to Germany, while at least 270 have been killed in Iraq or Syria.
“A low three-digit-number” are currently detained in the two countries, according to the intelligence services’ 2021 report.