The Palestinian UN observer Riyad Mansour denounced on Wednesday Israel's legalization of three unsanctioned West Bank settler outposts as an illegal attempt to entrench "its massive network of illegal settlements."

The Palestinian condemnation is only the last in a wave of criticism Israel received after Prime Minister Benjamin Netanyahu announced that his government would seek to legalize the outposts’ status.

Open gallery view Houses in the West Bank outpost of Rechalim. Credit: Tomer Appelbaum

Mansour called on the UN Security Council "to act immediately to address these continuing illegal, grave actions by Israel."

He said in a letter to the council that the intensified construction of Israeli settlement activities in occupied Palestinian territory "is glaring proof" of Israel's "unlawful, expansionist aims."

Earlier on Wednesday, Catherine Ashton, the High Representative of the European Union for Foreign Affairs and Security condemned the move as well, saying that she was “extremely concerned.”Ashton called on Israel to reverse its decision.

“Settlements are illegal under international law, an obstacle to peace and threaten the viability of a two-state solution,” She said in her statement.

UN chief Ban Ki-moon said on Tuesday that he was "deeply troubled" by Israel's decision to grant legal status to three settlement outposts in the West Bank, describing the activity as illegal under international law.

Referring to three outposts - Bruchin, Sansana and Rechalim, Ban's office said in a statement that the "Secretary-General is deeply troubled by the decision of the Government of Israel to formally approve three outposts in the West Bank."

"The Secretary-General reiterates that all settlement activity is illegal under international law. It runs contrary to Israel's obligations under the Road Map and repeated Quartet calls for the parties to refrain from provocations," it said.

The United States also said it was "concerned by the reports" of Israel's decision. "We don't think this is helpful to the [peace] process, and we don't accept the legitimacy of continued settlement activity," said State Department spokeswoman Victoria Nuland.

Israeli officials played down the decision taken by a ministerial committee late on Monday and rejected accusations that the government had effectively created the first new Jewish settlements for more than 20 years.

The United Nations views all Jewish settlements in the West Bank as illegal. However, Israel distinguishes between settlements it has approved and the outposts that were never granted official authorization.

Some 350 settlers live in Bruchin and 240 in Rechelim, both in the northern part of the West Bank, while Sansana, with a population of 240, lies further to the south.

Earlier this month, the Quartet - the European Union, Russia, the United Nations and the United States - criticized Israeli settlement building and called on donors to meet aid pledges to the Palestinians as they sought to revive stalled peace talks.