Two sisters from the Gaza Strip were arrested Wednesday after they were caught smuggling explosives for Hamas in medical supplies, the Shin Bet security service said.

The women were caught at the Erez crossing when they left to Gaza after one of them had received treatment in Israel for cancer. The two were taken in for questioning and the explosives, which were hidden in tubes, were dealt with by a police expert in bomb disposal.

A preliminary investigation found that Hamas was behind the attempt and the explosives were intended for terrorist attacks in Israel, the Shin Bet said in a statement.

“This is a continuation of the attempts by terrorist organizations in Gaza, mainly Hamas, to abuse the humanitarian channel and the medical aid Israel provides to Gaza residents to carry out terrorist attacks in Israel,” the Shin Bet said.