The speaker of the Iranian parliament has lashed out at the US president over his refusal to certify the Iran nuclear deal agreed in 2015 by the members of the P5+1 group of world powers.

US President Donald Trump has shown that he doesn't abide by international agreements and obligations, the speaker of the Iranian parliament, Ali Larijani, said on Sunday, commenting on Washington's decision not to certify the Iran nuclear deal, paving way for a possible exit from the agreement in the future.

"It seems that Mr. Trump not only does not adhere to international agreements, but does not feel respect for the UN and demonstrates to all countries that the US government will not adhere to any obligations," Larijani said.