WASHINGTON -- US President Barack Obama on Tuesday said his administration wanted to see all countries sign the Nuclear Non-Proliferation Treaty, including Israel.

At the end of a 47-nation nuclear summit that Israeli Prime Minister Benjamin Netanyahu declined to attend, Obama was asked about Israel's refusal to join the NPT even as Washington works to bolster enforcement of the treaty.

"As far as Israel goes, I'm not going to comment about their program," Obama told a news conference.

But he said that "whether we are talking about Israel or any other country, we think that becoming part of the NPT is important."

That was a long-held US position that preceded the current administration, Obama added.

Foreign military experts believe Israel has an arsenal of several hundred nuclear warheads, but Israel has never publicly acknowledged it has nuclear weapons and has maintained a policy of deliberate ambiguity.

Israel, like nuclear-armed countries India, Pakistan, and North Korea, is not a signatory to the nuclear NPT to avoid international inspections.

Obama's comments came after Prime Minister Netanyahu abruptly pulled out of the nuclear summit last week, and amid the worst tensions between the two allies in years.

Israeli media said Netanyahu was concerned that Muslim nations attending the conference planned to press for Israel to open its own nuclear facilities to international inspection.

Netanhayu's decision underscored Israeli reluctance to expose its own nuclear programme to scrutiny, even as it voices growing concern over Iran's nuclear ambitions.