U.S. President Barak Obama's chief adviser on counter-terrorism, John O. Brennan, was in Israel to hold talks on the recent terror attack against Israelis in Bulgaria and the threat of al-Qaida involvement in the Syrian crisis, Ha'aretz daily reported on Thursday.

The talks were held on Wednesday between Brennan and head of Israel's National Security Council (NSC), Brig.-Gen. (ret) Yaakov Amidror, Eitan Ben-David, head of NSC Counter-Terrorism Bureau, and senior officials of the Mossad, the Shin Bet security service and the Israel Defense Forces Intelligence Branch.

The main subject of the meeting, a U.S. senior official told the daily, was the progress made so far on disclosing the identity of the suicide bomber that killed five Israelis a week ago in Burgas, Bulgaria.

As of now, the U.S. intelligence service, which is collaborating with its Israeli, Bulgarian counterparts, is still clueless about the identity of the suicide bomber and no clear evidence has been provided yet to sustain U.S. and Israeli claims that Iran, Hezbollah, are behind the attack.

Brennan also discussed recent U.S. suspicions of al-Qaida extremists infiltrating into Syrian rebel troops, and the dangers this could pose to Israel.

The talks also revolved around weapon smuggling from Egypt into the Gaza strip and the lack of security in the Sinai Peninsula.

Brennan is one of Obama's closest security advisers and is a CIA veteran, having served as head of National Counter-terrorism Center in the agency.