Danish broadcaster DR said the teenagers, aged 16 and 19, are suspected of acting "in association and together with prior agreement with one or more perpetrators."
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Two Swedish teenagers have been arrested at Copenhagen train station in connection with two explosions near the Israeli Embassy in the Danish capital on Wednesday.
Prosecutors said investigators were working to establish "whether the motive could be a terror attack."
No one was injured in the pre-dawn blasts which happened in a neighbourhood that is home to several foreign diplomatic missions, although the nearby Jewish school was closed following the explosions.
The pair, who cannot be identified under a court order, were ordered to be held in pre-trial detention for 27 days.
They faced preliminary charges of possessing illegal weapons and carrying five hand grenades.
Two of the grenades blew up when the suspects threw them at a house near the embassy, prosecutor Søren Harbo said.
"This was pretty close to the Israeli Embassy," Harbo said before Thursday's court hearing. The explosions caused damage to the roof terrace of a nearby house.
The diplomatic mission was not damaged.
Thursday's hearing was held behind closed doors after the preliminary charges were read.
Reporting from inside the court room, Danish broadcaster DR said the teenagers, aged 16 and 19, are suspected of acting "in association and together with prior agreement with one or more perpetrators."
Both denied the charges, local media reported.
The two suspects were arrested shortly before noon on a train at Copenhagen central station on Wednesday.
Danish media ran photos of a man in a white hazmat suit being taken away by police on a train platform at the station.
A third suspect, aged 19, who had been arrested near the embassy, has been released, police said.
In Denmark, the charges are one step short of formal charges and allow authorities to keep criminal suspects in custody during an investigation.
Shots fired in Stockholm
Separately, shots were fired late on Tuesday at the Israeli Embassy in Stockholm. No one was injured and no arrests have been made.
The Danish domestic security service, known by its acronym PET, said that "Swedish authorities have assessed that at least one specific act directed at the Israeli embassy in Stockholm, which was carried out by young criminals in Sweden, has links to Iran."
In May the Swedish domestic security agency SAPO accused Tehran of using established criminal networks in Sweden as a proxy to target Israeli or Jewish people.
In a statement, PET said, "if we have a state actor who gets young criminals to carry out actions aimed at Jewish targets in our neighbouring country, then we can be concerned that this will also happen in Denmark."
Speaking in Copenhagen on Thursday, Denmark's Prime Minister Mette Frederiksen said it was becoming increasingly dangerous to be a Jew in Europe.
"Antisemitism is on the rise. I can't distance myself enough from this and just say to both Danish Jews and everyone else who cares about their well-being, fortunately, many of us do, that the authorities are doing everything they can to protect the Jewish minority in Denmark," she said.