DHAKA, April 30 (Xinhua) -- Members of Bangladesh's major opposition party have, in a surprise move, taken the oath of office.

Bangladesh's Parliament Speaker Shirin Sharmin Chaudhury swore in the four lawmakers at a ceremony in the capital Dhaka on Monday.

Ex-Prime Minister Khaleda Zia's Bangladesh Nationalist Party (BNP) which suffered the most lopsided loss in its political history since 1978 won only six seats in the December 2018 parliament polls and skipped the Jan. 3 oath-taking ceremony.

Eight MPs from Khaleda Zia's BNP-led major opposition alliance skipped the oath-taking ceremony of new lawmakers.

Also they did not attend a ceremony where Bangladeshi Prime Minister Sheikh Hasina was sworn in on Jan. 7 for her third straight five-year term.

Another BNP-lawmaker elect took oath as MP on April 25 against the party's former decision of not joining parliament.

BNP Secretary General Mirza Fakhrul Islam Alamgir was the only influential leader of the party who won the election.

Fakhrul, who opted out despite four MPs-elect of his party took oath on Monday, said MPs-elect took oath of office on instructions from BNP acting chief in exile Tarique Rahman, the elder son of BNP chief Khaleda Zia, who has been staying in London since 2008.

BNP rejected the 2018 election results, alleging various irregularities.

According to the Election Commission Gazette, Awami League (AL) led by Hasina won 257 out of 300 seats, more than enough for her party to form a straight third five-year term government since January 2009 after ruling the country in 1996-2001.

BNP was the ruling party in Bangladesh for two terms -- 1991-1996 and 2001-2006 -- since the country's return to civilian government in 1991.

AL's key ally in the elections Jatiya Party won 20 seats while BNP's ally Gono Forum managed only two seats.

Ex-PM Khaleda Zia, also chairperson of BNP, who has been in jail since February last year in a corruption case could not join the polls.