Israeli Prime Minister Benjamin Netanyahu called on Tuesday for "increased pressure" on Iran, saying it was the "only thing" that would deter it from pursuing a nuclear weapons capability.

He was addressing a delegation of 36 visiting US Congressmen after Iran's new President Hassan Rowhani called for "serious" talks without delay to allay concerns about Iran's nuclear programme.

"Iran's president said that pressure won't work," Netanyahu told the delegation led by House Democratic whip Steny Hoyer.

"Not true! The only thing that has worked in the last two decades is pressure. And the only thing that will work now is increased pressure," Netanyahu said in remarks relayed by his office.

Rowhani had warned that negotiations would not work under pressure and had taken strong issue with a letter signed by 76 US senators calling for tougher sanctions.

The new Iranian president charged that the letter was the work of a "foreign country" and its supporters in the United States, in a clear allusion to Israel.

Despite Iran's denials, Netanyahu has repeatedly accused it of seeking a nuclear weapons capability, which he has said would constitute an "existential threat" to Israel.

"I have said that before and I'll say it again, because that's important to understand," Netanyahu told the US lawmakers.

"You relent on the pressure, they will go all the way. You should sustain the pressure."

Both the United States and Israel -- which has the Middle East's sole, if undeclared, nuclear arsenal -- have refused to rule out a resort to military action to prevent Iran developing a weapons capability.