Iranian police said that continuing to chase suspects who had fled into Pakistan was the normal procedure.
Dadur Raman, a Pakistani police officer, said that two vehicles had been seized.
It was not made clear by Pakistani authorities when those detained would be released.
The incident comes after six Revolutionary Guards were among 42 people killed eight days ago by a suicide bomber on the Iranian side of the border near Pishin, in Sistan-Baluchestan province.
Mahmoud Ahmadinejad, Iran's president, said that some Pakistani intelligence officers had supported a Sunni group known as Jundollah (Soldiers of God), who had claimed responsibility for the attack.
Iran has said Jundollah operates from across the border in Pakistan.
Islamabad, which usually has good relations with Tehran, has denied both claims and denounced the bombing, saying that it would help to find the perpetrators.