The UN Security Council on Wednesday expressed great sympathy for the victims of Monday's Boston Marathon bombings, which left three people dead and at least 170 others injured.

Before the start of an open debate, Rwandan Foreign Minister Louise Mushikiwabo, whose country holds the rotating presidency of the Security Council for April, voiced the 15-nation UN body's " deepest sympathy" for the victims of the "senseless killings" in Boston.

Reading out a brief message, the Rwandan minister also extended sympathy to "the (victims') families, the people and the government of the United States" on behalf of the Security Council.

Twin explosions occurred near the finish line of the Boston Marathon on Monday afternoon, causing heavy casualties. Among those killed were an eight-year-old boy and a female Chinese student studying in a Boston university.

The U.S. authorities have called the bombings an "act of terror, " but the motives and perpetrators remain unknown.

On the same occasion, the UN Security Council also paid tribute to late British prime minister Margaret Thatcher, who died of a stroke on April 8 at the age of 87 and whose funeral took place in London on Wednesday.