The European Central Bank (ECB) Executive Board Member Benoit Coeure said on Tuesday that the ECB plans to expand its asset purchases in May and June due to low market liquidity in July and August.

"If need be, the frontloading may be complemented by some backloading in September when market liquidity is expected to improve again", he added.

Coeure noted that a selloff in the European government bond market was a normal correction, but the pace of the selloff was worrisome.