BRUSSELS, Belgium - The European Union on Tuesday expressed unease that parliamentary elections in Bangladesh did not have opposition representation because of a boycott, and called for alleged polling irregularities to be investigated.

"The EU regrets that not all major parties participated in this election," the bloc's foreign policy chief Josep Borrell said in a statement that "takes note of the outcome".

The opposition boycott and mass arrests dogged the elections held on Sunday in the South Asian country, which saw Bangladeshi Prime Minister Sheikh Hasina handed a fifth term after her ruling party took three-quarters of the parliamentary seats.

The EU "will continue to work" with Hasina's government in various priority areas, Borrell said.

But he stressed that "the long-term EU-Bangladesh partnership is underpinned by the values of democracy, human rights and the rule of law".

On Monday, the US State Department also expressed regret that not all parties were represented and said "these elections were not free or fair".

China congratulated Hasina's party on its victory.

Borrell pointed to a report by EU election experts that he said Bangladeshi authorities had agreed to make public, adding: "We call upon the relevant authorities to ensure a timely and full investigation of all reported election irregularities."

The EU, he said, "condemns the acts of violence that occurred during the electoral period and urges everybody to refrain from violence in the post-election period".

He also said that "the detention of opposition figures is highly concerning" and encouraged all political forces in Bangladesh to respect "political pluralism, democratic values and international human rights standards".