German police arrested three men in the eastern city of Chemnitz on Saturday in connection with a raid of a flat earlier that day over a suspected bomb attack.
The three are suspected of being linked to a 22-year-old Syrian who fled from authorities after police found several hundred grams of explosives in the flat.
The city's central train station was temporarily on lockdown after police arrested two of the men there. A special police robot was deployed to test a suitcase carried by the two men, according to regional police, but the baggage was found not to be dangerous.
Police said they had meanwhile launched a manhunt for the 22-year-old Syrian, identified as Jaber al-Bakr, across the eastern state of Saxony. Security sources told dpa there was a suspected connection to the Islamic State extremist group.
"We want to find him as soon as possible," regional police spokesman Tom Bernhardt said.
Local police were informed about a "serious threat" by German intelligence on Friday night, Bernhardt said.
Hundreds of additional police have been deployed in the German capital Berlin and extra security precautions have been installed at Berlin-Schoenefeld airport.
In addition to added personnel, buses were no longer allowed to drive into the terminal at the airport.
Cars and buses were also being stopped and searched for the suspect al-Bakr.
Suspicions of a planned bomb attack led special forces to put a high-rise apartment block on lockdown for several hours on Saturday.
Special forces stormed the apartment around 1 pm (1100 GMT) to find the rooms empty.
It was initially unclear if al-Bakr arrived in Germany as a refugee. Some 890,000 migrants arrived in the country in 2015, many of whom had fled the ongoing conflict in Syria.
Germany has been on high alert since two terrorist attacks occurred over the course of one week in July. Both were claimed by Islamic State militants and carried out by asylum seekers.
At least five Islamist attacks have been thwarted by German police since the year 2007.