BERLIN (Reuters) - German Foreign Minister Guido Westerwelle urged the mayor of Berlin on Friday to tighten security at foreign embassies in the city, a day after 30 protesters stormed the grounds of the Iranian mission and pelted the building with stones.

Westerwelle asked mayor Klaus Wowereit in a letter to act swiftly to remedy security shortcomings, citing 13 occasions over the past two years when embassies, including those of Libya and Nigeria, were attacked or occupied.

"Just as we expect other states to provide adequate protection for our embassies, so we must ensure German authorities are doing everything possible to protect diplomatic missions," Westerwelle's spokesman said on Friday.

Berlin police said in a statement that masked protesters used rope-ladders on Thursday to climb into the grounds of the Iranian embassy, where they tore down a flag and torched it, and defaced the building.

Police officers assigned to protect the building were overwhelmed and threatened by the protesters.

A spokesman for Wowereit said embassies were receiving suitable protection.

(Reporting by Alexandra Hudson; Editing by Sophie Hares)