File photo shows Nigerian President Muhammadu Buhari (C) waving to audiences during his inauguration ceremony in Abuja, Nigeria, May 29, 2015. (Xinhua/Yang Yang)

ABUJA, Feb. 22 (Xinhua) -- Nigerian leader Muhammadu Buhari on Tuesday allayed fears of the country's citizens over his prolonged vacation in the United Kingdom, saying "there is no cause for worry."

An official statement made available to Xinhua did not say exactly when the vacation embarked on by the Nigerian leader would be over.

"During his normal annual checkup, tests showed he needed a longer period of rest, necessitating the President staying longer than originally planned," said the statement signed by presidential spokesman Femi Adesina.

Buhari jetted out of the west African country on Jan. 19, proceeding on a 10-day vacation as part of his 2017 annual leave and had planned to resume official duties on Feb. 6.

The president was scheduled to return to Abuja, the Nigerian capital, on the evening of Feb. 5 but was advised to complete and receive the results of a series of medical tests recommended by his doctors before returning, he personally wrote in a notice dispatched to the Senate President and Speaker of the Nigerian House of Representatives.

Buhari's prolonged absence still continues to cause tongues wagging in the country, with opposition groups insisting on the official disclosure of his real health status.

Ahead of his vacation, Buhari had transmitted a letter to the Senate, requesting that his Vice-President, Yemi Osinbajo, be empowered to act as President until his return and in accordance with the provision of the country's constitution.

Early this month, a rumor of the president's death had spread like a wildfire, causing Panic among citizens.

Many did not take the rumor of Buhari's death funny. A police investigation is underway to uncover and prosecute the masterminds of the rumor.

Some citizens even offered special prayers in their respective worship places for the president's good health.

In the statement issued Tuesday, Buhari thanked millions of Nigerians "who have been sending good wishes and praying for his health and well-being in mosques and churches throughout the country."

"The President is immensely grateful for the prayers, show of love and concern," the statement added.

Buhari's media aides insist he is not ill amid the controversy in which speculations had also risen that the president was battling a terminal illness.

On June 6, 2016, Buhari had traveled to London to have a short rest and see an Ear, Nose, and Throat (E.N.T) specialist for a persistent ear infection after being examined by his personal physician, according to Adesina.

Nigeria's main opposition Peoples Democratic Party (PDP) had urged the president to address the nation, particularly on the sudden extension of his vacation and his present health status, to douse tension in the country.

The opposition group, noting the president is not a private citizen, demanded a full disclosure of the reason the president is still holding back in the UK.

"Imagine the president talking about a leave extension but not saying about when he would resume. Medical tests have dates of collection of results. It can't be open-ended without dates," the Nigerian opposition party said in a statement made available to Xinhua.

Adesina said so long as there was no vacuum in government, the president can take the time he desired until his doctors give him a clean bill of health before returning home.

"There's no lacuna because power has been transferred to the vice-president who is acting president," he added.