Palestinian President Mahmoud Abbas on Monday announced a three-day mourning in the Palestinian territories and refugee camps in neighboring Arab countries after the death of more than a dozen pro-Palestinian activists when Israeli naval forces attacked Gaza aid flotilla.

In a phone interview with the official Palestinian television, Abbas, who is visiting Jordan, ordered the national flag to be lowered at half-mast to express condemnation and grief of "the Israeli crime."

"It was a complex aggression in which those who aid the Palestinian people in Gaza, which is besieged from the outset by Israel, were killed," Abbas said.

Abbas said he is "following up the situation very carefully," he also called on the United Nations "to stand in the face of Israel which throws away all international laws and customs."

Early Monday morning, the Gaza Strip, which has braced for receiving the flotilla, woke up to a state of frustration following the news that the Israeli navy attacked the ships that carry hundreds of pro-Palestinian supporters and 10,000 tonnes of aid to the besieged enclave.