BEIRUT (Reuters) - Lebanon’s caretaker prime minister, Hassan Diab, has declined to be questioned by the judge who charged him and three former ministers with negligence over the Beirut port blast, an official source said on Monday. Judge Fadi Sawan has met pushback from influential parties including Shi’ite Hezbollah and Sunni leader Saad al-Hariri, underlining the political hurdles facing the investigation. Lebanese are still waiting for answers four months since one of the biggest non-nuclear blasts on record. A stockpile of ammonium nitrate, stored unsafely for years, detonated in August, killing 200 people, injuring thousands and devastating entire districts. Some politicians accused Sawan of being selective and overstepping his powers by charging ministers. Others, including the head of the Beirut Bar Association, said the move showed courage. The outgoing premier “has said everything he has to say about this file, full stop,” according to his office. Diab, who has testified as a witness, quit after the disaster but continues to serve in a caretaker role. He and President Michel Aoun were warned in July that the nitrate could destroy the capital if it exploded, according to documents seen by Reuters. Aoun has said he had no direct authority over the port. Sawan requested an appointment from Diab’s office but was told he would not agree to be questioned, the official source at the prime minister’s office said. Sawan could not immediately be reached for comment. The caretaker interior minister, Mohammed Fahmi, said he would not enforce any arrest warrants for Diab or the other officials if they refused to be questioned. “And let them pursue me if they wish,” Lebanese newspaper al-Joumhouria quoted him as saying. After meeting with Diab on Friday, Hariri pledged not to let anyone “violate the post of prime minister” - a seat reserved for a Sunni Muslim in the sectarian power-sharing system. The ex-ministers charged by Sawan are members of parties allied to Hezbollah, which said the charges smacked of “political targeting”. Two are from Parliament Speaker Nabih Berri’s Shi’ite Amal party, which also accused the judge on Monday of breaching the constitution. Lebanon’s senior Christian cleric, Maronite Patriarch Bechara Boutros Al-Rai, said on Sunday he hoped reactions to Sawan’s move would not obstruct the probe or cause “a national division on a sectarian basis”.