The number of Israeli settlers in the occupied West Bank has passed the 350,000 mark for the first time, after increasing by more than 15,500 in the past year alone.

New population figures for the settlements – regarded as illegal in international law by most of the world, including Britain – have been welcomed by a prominent settler leader as evidence that their presence is an "irreversible fact".

The official interior ministry figures, obtained by the right wing daily newspaper Israel Hayom, do not include nearly 200,000 Jewish settlers in East Jerusalem districts seized in the 1967 Six Day War and also regarded as illegal by most of the international community.

The figures came to light the day after the Palestinian Prime Minister, Salam Fayyad, spoke in an interview in The Independent yesterday about the West's failure to do more to halt the expansion of settlements in clear breach of the 2003 internationally agreed Road Map for Israeli-Palestinian peace. In stark contrast, the figures were warmly welcomed by the Israeli pro-settlement right wing, with Dani Dayan, leader of the settlers' umbrella body the Yesha Council, calling on "the American government and its European allies" to abandon the "failed formula" of a two state solution and accept that the "Jewish residents of Judaea and Samaria [West Bank] are not going anywhere."

In a New York Times op-ed article, Mr Dayan said the increase in settlers – to almost double their numbers in 2000 – had been "wise" because the "insertion of an independent Palestinian state between Israel and Jordan would be a recipe for disaster."

The breakdown of the figures are significant because they show that both the highest growth in the last year and the highest numbers overall are outside the so-called settlement blocs which an Israeli "consensus" assumes would be assigned to Israel in any agreed deal with the Palestinians.

That means that the increase is disproportionately high in those settlements which it is assumed would have to be evacuated in any such deal and whose residents are therefore likely to be most vigorously opposed to one. According to the breakdown, a total of 116,824 Israelis live in the main settlement blocs, while more than 233,000 live outside them. But even that figure underestimates the potential numbers that might have to be moved under any deal, since the blocs include Ariel, now the largest settlement with 50,000 residents.