BEIRUT, Lebanon (CNN) — Under pressure from the United Nations and opposition politicians, Lebanon’s security chief said he was putting his fate in the hands of Prime Minister Najib Mikati.Friday’s move was a step short of resignation and comes ahead of a U.N. authorized investigation into the assassination of former Prime Minister Rafik Hariri.Jamil Sayyed, head of general security in Lebanon, said he was putting himself at the disposal of the prime minister, leaving it up to Mikati to decide his fate. The Associated Press reported that Ali Hajj, the country’s top police commander, also has stepped aside and placed himself at Mikati’s disposal. Hajj told AP he was taking the step “to facilitate the work of the international investigation commission until the end of its mission.” He said it was up to the Cabinet to decide whether to reinstate him later.

Meanwhile, Mikati said key elections will be held by May 29, two days before parliament’s term ends — the first time a government leader has given a specific date for the vote, AP reported.

He told reporters he was sending to the legislature a proposed mechanism to hold elections within the constitutional deadline. If parliament does not approve the mechanism, his Cabinet will call an election on its own, he said.

“If the honorable parliament does not approve, we will be forced to call the electoral bodies a month before May 29, that is April 29, in order to conduct elections on May 29,” AP quoted Mikati as saying.

Lebanon has been in a political crisis since Friday, when Hariri was killed in a car bombing. The assassination prompted large-scale demonstrations calling for Syria to leave the country.

Opposition groups have called on Lebanon’s top security officials, all considered to be pro-Syrian, to resign.

Hariri was a key mover in getting a U.N. resolution to call on Syria to remove its troops and intelligence assets from Lebanon. Resolution 1559, passed last year, also calls on Lebanon to disband guerrilla groups.

Now Hariri’s death is at the center of an international investigation authorized by the U.N. Security Council. The investigation is expected to begin in the coming weeks.

A U.N. report released last month said the government of Syria “interfered” with governance in Lebanon in a heavy-handed way that was “the primary reason for the political polarization that ensued” before Hariri’s death.

“It is obvious that this atmosphere provided the backdrop for the assassination of Mr. Hariri,” the report said.

The Lebanese opposition has gone further, saying his assassination was an act of political retribution by Syria.

Syria’s government has said it had nothing to gain and everything to lose from Hariri’s death.

Yet faced with increasing international pressure, the country has agreed to withdraw its forces from Lebanon by April 30, ahead of parliamentary elections in May.

Syria began pulling its 14,000 troops to the Bekaa Valley near the border March 8.

Syria has had a presence in Lebanon since the end of its 15-year civil war, which mostly pitted Lebanon’s ruling conservative Christians against leftist Muslims, with Syria, Israel and Western international forces — including U.S. Marines — occasionally taking part.

The treaty that ended the fighting revised the constitution to give the Muslim majority a greater role. The presidency, chosen by parliament, goes to a Christian. The prime minister must be a Sunni Muslim.