Two Palestinian sisters from Gaza have been caught trying to smuggle explosives hidden in medicine containers into Israel as they were headed for cancer treatment at a Jerusalem hospital, authorities say.

Israeli authorities believe Hamas militants were trying to use the pair to carry out an attack.

In a statement, the Shin Bet security agency said the women, who had entry permits to Israel for medical treatment, were caught on Wednesday.

Ragheb Atallah, the patient's husband, said his wife, Basema, 55, has gone for treatment of colorectal cancer in Jerusalem more than 10 times since July and has never had a problem before.

He said his wife was unaware that she may have been smuggling anything illegal into Israel.

"Someone asked them to take a bottle of medicine on their way for a patient there," he said.

"The bottle was closed and they did not know what is inside. It seems there was something and this caused disruption."

Mr Atallah said his wife was released and has been given permission again to go to the hospital, but her sister, 57-year-old Ibtessam Eid, remained in Israeli custody.

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Israel and Egypt imposed a blockade on Gaza after the Islamic militant group Hamas seized power in the coastal strip from forces loyal to Palestinian President Mahmoud Abbas in 2007.

Since then, Israel and Hamas, which is sworn to Israel's destruction, have fought three wars.

Gazans wishing to enter Israel for medical care or to travel to neighbouring Jordan and other destinations are subject to strict security checks, including in some cases lengthy interrogations by Shin Bet agents before they receive travel permits.

Israel says the strict policies are necessary because Hamas tries to exploit civilians entering Israel by giving them weapons, cash or other equipment for militant activity.

There was no immediate comment from Hamas.

AP