GAZA - Israeli navy on Saturday intercepted a Finnish-flagged boat carrying pro-Palestinian international activists about 40 miles away from the Gaza Strip's coast, a Palestinian official said.

"The crew of Estelle said that a number of Israeli vessels surrounded the boat in the regional waters," said Mustafa al- Barghouti of the Palestinian National Initiative. He was speaking from the West Bank on telephone and was on constant contact with the activists onboard.

The aim of the ship is to challenge Israel's naval blockade on the Gaza Strip. It carries symbolic humanitarian aid and activists from Europe and Canada, including some parliamentarians.

Al-Barghouti said that Israel has threatened the activists to storm the boat and arrest them if they continued their voyage to the Hamas-controlled Gaza.

Amjad al-Shawa, head of the Palestinian Non-Government Organizations Network (PNGO), said that the activists told him they were determined to make it to Gaza.

The set sail from Sweden three months ago, making stops in several European ports to pick up the activists and the aid.

Last week, Israel notified Finland that the boat will be stopped if it tried to enter Gaza's waters.

In 2008, several international ferries succeeded to dock at Gaza's fishing harbor, a year after Israel imposed a strict ground and naval blockade in Gaza to isolate Hamas.

But following Israel's major military offensive here in 2008-09 winter, Israel decided to ban all foreign ships from entering Gaza 's waters.

In 2010, Israeli commandos intercepted a Turkish flotilla bound for Gaza and killed nine Pro-Palestinian Turks, tensing diplomatic relations between Israel and Turkey. Following the standoff, Israel relaxed the overland closure, but kept the naval blockade tight.