US Secretary of State John Kerry arrived in Brussels on Friday to show solidarity and offer US assistance after Tuesday's Islamic State-claimed bombings which killed 31 people and injured about 270.

Kerry, travelling from Moscow, landed at Brussels airport where one of Tuesday's attacks occurred.

He will meet with Belgian officials including Prime Minister Charles Michel and Foreign Minister Didier Reynders, as well as EU Commission President Jean-Claude Juncker. Before departing, he will lay a wreath at the site of the airport attack.

Two government ministers offered to step down over security lapses that have drawn international criticism of an apparent reluctance to tackle Islamist radicals effectively, but Prime Minister Charles Michel rejected their resignations.

Kerry will repeat a US offer to help with the investigation and efforts to fight terrorism.

Brussels is a large diplomatic and military base for Americans working at US missions in the city as well as at the European Union and NATO.

About a dozen Americans were among those hurt in the attacks, although it is not clear if any were killed.

The attacks came four months after Islamic State militants carried out bombings and shootings in Paris that killed 130 people.