A construction site for a new neighborhood is seen on July 18, 2013 in the Israeli settlement of Ariel in the West Bank. Uriel Sinai/Getty Images

Construction on new homes in Israeli settlements in the occupied West Bank spiked by 70 percent in the first half of 2013, an Israeli NGO reported Thursday — raising worries that peace talks, which renewed in July after a three-year lull due to ongoing disputes over settlement building, could falter.

According to Peace Now, which tracks settlement activity in Palestinian territory Israel captured in the war of 1967, construction began on 1,708 settlement homes from January to June of this year, compared with 995 during the same period in 2012.

Moreover, it said that 61 percent of the construction took place in isolated settlements outside larger settlement blocs that Israel has said it intends to keep in any future land-for-peace deal.

Settlements built on Palestinian territories occupied by Israel, including East Jerusalem, are deemed illegal by the United Nations, and insistence that Israel demonstrate good faith by halting such construction had been a key reason for the Palestinian side declining to reenter peace talks over the past three years.

An estimated 500,000 Israelis currently live in fortified Jewish-only settlements in the Palestinian territories, home to 2.5 million Palestinians.

In May, Israeli media reported that Prime Minister Benjamin Netanyahu had ordered a freeze in tenders for new housing projects in West Bank settlements in an apparent attempt to help revive U.S.-backed peace talks.

However, on the eve of the resumed talks Israel approved 942 new settlement housing units in East Jerusalem.

Mark Regev, spokesman for Israeli Prime Minister Benjamin Netanyahu, insisted at the time that the new settlement units were being built "in areas that will remain part of Israel in any possible future peace agreement."

"It changes nothing," he added.