The Whitechapel Gallery in London's East End has marked a £13.5 million expansion by welcoming a version of Picasso's anti-war work Guernica, 70 years after the original was shown there.

Turner Prize-nominated artist Goshka Macuga helped convince Margaretta Rockefeller to lend the Whitechapel the 20ft long tapestry for a year, which has been on long-term loan in the United Nations building in New York since 1985.

It was commissioned by tycoon Nelson Rockefeller, Margaretta's late husband, in 1955.

Seventy years ago Picasso's monumental painting, which depicts the 1937 Nazi bombing of the Basque town of Guernica during the Spanish Civil War, was shown at the Whitechapel for two weeks, attracting 15,000 people.

Polish-born Macuga, 42, said she was inspired to revive the spirit of that event.

Knowing that the Museo de Arte Reina Sofia in Madrid would not agree to let the painting travel, the Whitechapel approached the Rockefeller family.

Macuga said the tapestry had been given extra significance as an anti-war symbol since Colin Powell delivered his flawed evidence on the apparent existence of weapons of mass destruction in Iraq in the run-up to the invasion in early 2003.

Then the Guernica tapestry, which normally hangs outside the UN Security Council chamber, was covered by a blue cloth - apparently to make television pictures of Powell clearer.

The excuse fooled no one.

Macuga said: "If you are starting a war you are not going to do it in front of an anti-war symbol."

To accompany the tapestry, Macuga created a hollow round-table for people to hire for discussions, filled with war and anti-war propaganda. She commissioned a bronze cubist-style bust of Powell, which she said represented "a figure who is falling apart morally". In 2004 Powell admitted the evidence he submitted to the UN on WMDs could have been wrong.

The commission, sponsored by Bloomberg, marks the gallery's reopening after its £13.5 million Heritage Lottery Fund-sponsored refit, which has almost doubled its exhibition space.

Iwona Blazwick, the Whitechapel's director, said: "The expansion enables us to be open all year round so there will always be something for free to see."

It reopens to the public on April 5.